Design Criteria for Swine Waste
Flushing Systems
Prepared by:
James C. Barker
Professor and Extension Specialist
Biological and Agricultural Engineering
L. Bynum Driggers
Professor and Extension Specialist
Biological and Agricultural Engineering
Ronald E. Sneed
Professor and Extension Specialist
Biological and Agricultural Engineering
North Carolina State University, Raleigh, NC
Published by: North Carolina Cooperative Extension Service
Publication Number: EBAE 080-81
Last Electronic Revision: March 1996 (JWM)
North Carolina swine production has consistently moved toward large confinement operations with
animals housed in environmentally controlled or curtain side-walled buildings over concrete slab
or slotted floors. Storage of waste for short periods of time on slab or for prolonged periods in
underslat storage pits was a substantial improvement in waste handling over previous methods or
drylot systems. Scraping or washing the solid floors often enough to prevent excessive odors
became labor intensive. Preventing manure solids from settling to the bottom of storage pits and
accumulating to the extent that they were difficult to agitate and remove became a management
crisis for many producers. As anaerobic decomposition produced more odor and gases within the
building, herd health and animal performance suffered.
Since lagoon treatment of animal wastes is widely utilized in the Southeast, recycling of lagoon
effluent appeared to be the next step in expanding waste handling technology. For these reasons,
waterwash (flush) systems have become quite popular over the last decade for frequent removal of
wastes from underfloor pits and open floor gutters to a storage basin or lagoon (figure 1). Frequent
loadings by flushing also enhance lagoon performance.
Advantages Several advantages result from frequent removal of wastes and associated anaerobic
contaminants from production buildings. Reduced pit gases and odor improves the in-house
environment, animal health and performance and employee working conditions. A reduction of these
odorous gases exhausted from the building by pit ventilation systems is likely to reduce the potential
for nuisance complaints. The solid buildup in the bottom of storage pits is no longer a handling
problem, thereby improving labor and management efficiency. Corrosion and maintenance
requirements by metallic components of the building are reduced. The capital costs of installing flush
systems in new buildings is somewhat offset by the shallower underfloor pits required.
Ventilation Flushing technology should not become a substitute for ventilation. The primary purpose
of ventilation is to remove moisture from a building during the winter and to control temperature
during the summer. This basic requirement remains the same whether pits are flushed or not.
Therefore, even though the primary source of gas and odor generation has been reduced by flushing,
pit ventilation should still be provided.
Floor Type Flushing under slats or raised decks is recommended for all buildings while open floor
gutter systems are a possible alternative only for gestation buildings. Disease, parasites and antibiotic
transmission are potential problems where animals have direct access to the flush water.
Background Information on flush system design prior to 1980 was primarily confined to open gutter
buildings less than 125 feet (ft) long with a slope of 1-2%. Variable-width, variable-slope gutters
presented construction difficulties. Information for flushing longer buildings with wider underslat pits,
flatter uniform slopes, and varying animal densities was limited. This article presents design criteria
tailored toward individual building characteristics and constraints.
DESIGN PRODEDURE
Flow Rates Basic hydraulic rules were used to establish a link between channel slope, width and flow
rate required for gutter cleaning. A minimum flow velocity of 3 feet per second (fps) was assumed for
adequate cleaning. Table 1 presents minimum flow rates needed for varying flush channel slopes and
widths. A discharge duration of 10 sec is desirable; therefore, an additional column in Table 1
establishes this minimum flush tank size. This flush volume may not be the governing value, however,
as will become apparent in the following section. Table 2 lists pipe sizes or openings needed for
discharge rates at varying hydrostatic heads.
Flush Volumes Flush volumes can be determined by manure viscosity, solids carrying capacity of the
flush water, manure production or animal densities, and channel slope. A relationship can be
developed between the minimum viscosity for adequate waste removal and the dry matter content or
solids carrying capacity of the flush water. The waste density was assumed to be the same as water.
Laboratory studies were conducted to develop an empirical relationship between viscosity and dry
matter content in order to establish the solids carrying capacity of the water and correspondingly the
water volume needed for waste removal. The amount of manure solids to be removed from the gutter
can be determined from the animal densities and liveweights. The total mass including both the flush
water volume and the manure solids can now be estimated. The flush volume required is the
difference between the total mass and the weight of the manure solids. Table 3 presents tabulated
water volumes recommended for varyi ng channel slopes and flush frequencies.
Detailed design procedures and assumptions are explained by Barker and Driggers, 1980.
Table 1. Channel Flow Rates for Cleaning Velocity
______________________________________________
Channel
Channel
Flow
Flow
Min volume
slope
width
depth
rate
for 10-sec
discharge
______________________________________________
%
feet
inches
gpm
gallons
0.5
2
3.5
783
130
3
3.2
1070
178
4
3.0
1367
228
5
3.0
1666
278
6
2.9
1967
328
8
2.9
2571
428
10
2.8
3175
529
1.0
2
1.9
416
69
3
1.8
594
99
4
1.7
773
129
5
1.7
953
159
6
1.7
1132
189
8
1.7
1492
249
10
1.7
1853
309
1.5
2
1.3
295
49
3
1.3
427
71
4
1.2
560
93
5
1.2
693
115
6
1.2
825
138
8
1.2
1091
182
10
1.2
1357
226
2.0
2
1.0
233
39
3
1.0
340
57
4
1.0
447
74
5
1.0
554
92
6
1.0
661
110
8
1.0
875
146
10
1.0
1089
182
______________________________________________
FLUSH TANK SELECTION
Several types of automated flush tanks and discharge mechanisms have been utilized successfully in
North Carolina to deliver the required flush volumes at the desired flush frequencies. Tables 4 and 5
give the total water capacity of tanks of varying dimensions. A brief description of the more
frequently used flush tanks follows.
Table 2. Water Volume Required for Flushing
______________________________________________________
Channel
Number of flushes per day
Slope
_____________________________________________
1
2*
3
4
6
12
______________________________________________________
%
------gallons per 100-lb hog per flush-----0.5
3.21
1.61
1.07
0.80
0.54
0.27
1.0
2.97
1.48
0.99
0.74
0.50
0.25
1.5
2.84
1.42
0.95
0.71
0.47
0.24
2.0
2.75
1.38
0.92
0.69
0.46
0.23
______________________________________________________
* Recommended minimum flush tank design capacity.
Table 3. Flush Tank Discharge Rates
Hydro-Discharge
Nomimal Discharge Pipe Diameter, inches
staticPipe Exit ____________________________________________________________
Head Velocity
2
3
4
6
8
10
12
15
____________________________________________________________________________
feet ft per sec ____________________gallons per minute____________________
1
4.01
39
88
158
353
628
982
1416
2210
2
5.68
56
125
222
500
889
1389
2000
3126
3
6.95
68
153
272
612
1089
1702
2450
3828
4
8.02
78
177
314
708
1258
1964
2828
4420
5
8.98
88
198
352
791
1406
2197
3163
4942
6
9.82
96
217
385
866
1540
2406
3463
5414
7
10.62
104
234
416
936
1663
2599
3742
5847
8
11.35
111
250
444
1000
1778
2778
4001
6251
____________________________________________________________________________
Small-Diameter Single Siphon Figure 2 depicts this tank which offers automated dosing action with
no moving parts. At the beginning of the fill cycle, air is trapped under the bell. As the tank fills with
water, the air under the bell is slowly forced out of the siphon pipe until siphoning is triggered and the
tank empties. Tank materials can either be metal or concrete. These tanks have met with mixed
success since they are very sensitive to construction miscues and become impractical for long
buildings especially in the flatter Coastal Plain regions due to the steep pit slopes required for
cleaning. Table 6 gives construction dimensions.
Large-Diameter Multiple Siphon A larger, more successful version of the siphon tank (figure 3)
allows multiple large-diameter discharge pipes to emerge from a common ground-level tank and
siphon bonnet. Tank construction including the siphon bonnet is usually reinforced concrete. Initial
positioning of the 2-in siphon trigger tube and discharge pipe relative to the pit floor and tank floor is
important. This tank is more suited to flushing wider pits on flatter slopes. Table 7 gives construction
dimensions.
Tipping Bucket Rotating tilt tanks similar to the sketch in figure 4 dump when they fill with water to
a depth where the center of gravity is above the tank pivot point. Unless the tanks are constructed with
a lid and controlled discharge outlet, the water is discharged at once, and any manure remaining after
the first wave of water down the gutter will not be removed from the pit. These type of tanks are
recommended primarily for small volume applications such as farrowing houses or nurseries. Metal
tanks are expensive to construct, subject to corrosion, and require maintenance due to their frequent
violent rotations.
Valved or Gated Discharge These tanks offer the advantage of simple ground level reinforced
concrete or concrete and steel reinforced cinder block construction and the flexibility to either be
flushed manually or with commercially available flush gate mechanisms. These tanks may be built
adjacent to the end of the building using the building wall as a common wall to the tank or they may
be free-standing unattached to the building. Figure 5 depicts a simple and reliable water-weighted
valve opening mechanism which offers flexibility for opening multiple valves simultaneously at
varying valve diameters without requiring electromechanical actuation. Figures 5a through 5e show
the operating sequence of this valve opener and the adjustments necessary for it to function.
RECYCLE PUMPS
High-quality, low-pressure, self-priming centrifugal or submersible pumps control the filling of the
flush tanks with lagoon liquid. Avoid significant oversizing of pumps to minimize high flow velocities
through supply pipes and excessive turbulence in the pump cavity caused by throttling or valving the
discharge. The pump should have enough capacity, however, to allow it to operate only one-half to
two-thirds of the time. Consider placing the pump controls on a timer. Ensure that the suction line is
large enough to prevent pump cavitation. (Rule of Thumb: The suction pipe diameter should be one
standard size larger than the discharge pipe.) Also locate the pump as close to the high water level of
the lagoon as possible to minimize suction lift. The pump intake is generally an open-ended suction
pipe floating about 18 inches beneath the liquid surface of the lagoon. Remove fine mesh suction
intake strainers. Intakes may be screened by a 1-inch mesh wire fence or basket with a diameter a t
least 5 times the suction pipe diameter. The pump should be located as far as possible from the waste
input.
Table 4. Rectangular Tank Capacity
_____________________________________________________________________________
Tank
Tank Depth, feet
Width________________________________________________________________________
2
3
4
5
6
7
8
9
10
_____________________________________________________________________________
feet ____________________gallons per foot of tank length____________________
2
30
45
60
75
90
105
120
135
150
3
45
67
90
112
135
157
180
202
224
4
60
90
120
150
180
209
239
269
299
5
75
112
150
187
224
262
299
337
374
6
90
135
180
224
269
314
359
404
449
7
105
157
209
262
314
367
419
471
524
8
120
180
239
299
359
419
479
539
598
9
135
202
269
337
404
471
539
606
673
10
150
224
299
374
449
524
598
673
748
12
180
269
359
449
539
628
718
808
898
14
209
314
419
524
628
733
838
943
1047
16
239
359
479
598
718
838
958
1077
1197
18
269
404
539
673
808
943
1077
1212
1346
20
299
449
598
748
898
1047
1197
1346
1496
_____________________________________________________________________________
Table 5. Circular Tank Capacity
____________________________________________________________________________
Tank
Tank Depth, feet
Diameter ___________________________________________________________________
2
3
4
5
6
7
8
9
10
____________________________________________________________________________
feet
____________________gallons____________________
2
47
71
94
118
141
165
188
212
235
3
106
159
212
264
317
370
423
476
529
4
188
282
376
470
564
658
752
846
940
5
294
441
588
734
881
1028
1175
1322
1469
6
423
635
846
1058
1269
1481
1692
1904
2115
7
576
864 1152
1439
1727
2015
2303
2591
2879
8
752
1128 1504
1880
2256
2632
3008
3384
3760
9
952
1428 1904
2379
2855
3331
3807
4283
4759
10
1175
1763 2350
2938
3525
4113
4700
5288
5875
12
1692
2538 3384
4230
5076
5922
6768
7614
8460
14
2303
3455 4606
5758
6909
8061
9212
10364
11515
16
3008
4512 6016
7520
9024
10528
12032
13536
15040
18
3807
5711 7614
9518
11421
13325
15228
17132
19036
20
4700
7050 9400
11750
14100
16451
18801
21151
23501
____________________________________________________________________________
HIGH-VOLUME PUMP
Another technique which has been used effectively in North Carolina is a high-rate or high-volume
pumping system connected directly to a distribution header inside the building (figure 6). These
systems are especially useful for relatively flat slopes (<0.5%). These flat floors allow the capability
to maintain 1-2 in of water in the pit between flushes to prevent adherence of the manure to a dry
concrete floor. Recommended design pumping rates which have been field tested are 80 gpm per ft of
channel width for channel lengths up to 150 ft and 100 gpm per ft of channel width for channels
longer than 150 ft. Flow durations can be adjusted according to observed cleaning efficiency.
Table 6. Small-diameter single siphon dimensions
____________________________________________
Pipe
Symbol
diam. _____________________________________
a
b
c
e
f
g
h
i
____________________________________________
______________inches______________
2
36
48
1.5
5.0
1.0
6
9
48
60
1.5
6.0
1.0
8
9
60
72
1.5
6.5
1.0
9
9
3
36
48
1.5
6.0
1.0
9
11
48
60
1.5
7.5
1.0
12
11
60
72
1.5
8.5
1.0
14
11
4
36
48
1.5
8.0
1.0
14
12
48
60
1.5
7.5
1.0
12
14
60
72
1.5
8.0
1.0
13
15
6
36
48
2.0
9.5
1.5
18
16
48
60
2.0
9.5
1.5
17
18
60
72
2.0
9.5
1.5
16
20
8
36
48
2.5
9.5
2.0
17
22
48
60
2.5
9.5
2.0
17
24
60
78
2.5
11.5
2.0
20
24
____________________________________________
Table 7. Large Diameter Multiple Discharge Siphon Dimensions
Nom pipe
dia,in
4
6
8
_______________________________________________________________________________
No. disch
pipes
1
2 3
4
6
8
1
2
3
4
6
8
1
2
3
4
6
8
_______________________________________________________________________________
symbol
----------siphon dimensions, inches----------a
12 12 18 18 24 24 12 18 24 24 30 36 18 24 30 30 36 42
b
3.3 2.53.1 2.8 3.3 3.4 2.9 2.6 3.4 2.9 2.9 3.3 2.9 2.8 2.5 3.4 2.6 3.2
c
39 39 39 39 39 39 39 39 39 40 40 42 39 39 40 42 42 42
d
6.714.57.911.2 8.712.616.112.4 9.614.113.111.710.111.210.515.616.415.8
e
23 16 22 19 21 17 14 18 20 15 16 15 20 19 19 11 11 11
f
3
3 3
3
3
3
3
3
3
4
4
6
3
3
4
6
6
6
g
6 5.35.8 5.6 4.3 6.3 5.7 5.3 6.1 6.7 6.5 5.8 5.7 5.5 6.3 9.2 8.2 7.9
h
6
6 6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
Q*, gpm 293 589880117617622350 63712761903256438265101107921593268439065188691
_______________________________________________________________________________
Nom pipe
dia,in
10
12
____________________________________________________________________________
No. disch
pipes
1
2
3
4
6
8
1
2
3
4
6
8
____________________________________________________________________________
symbol
------------siphon dimensions, inches------------a
18
30
36
36
48
54
24
30
42
48
54
60
b
2.7 3.0
2.5 2.7
2.6
2.6
3.3 3.2 3.1 2.8
3.4
2.5
c
40
40
42
42
42
42
40
42
42
42
42
42
d
18.3 11.0 11.5 17.3 13.4 14.4 12.7 17.8 11.9 12.2
15.6 17.5
e
11
18
16
10
13
11
16
9
15
15
9
6
f
4
4
6
6
7
8
4
6
6
6
8
10
g
6.4 6.8
8.3 8.4
6.7
7.2
7.1 8.9 8.8 8.5
7.8
8.5
h
6
6
6
6
7
8
6
6
6
6
8
10
Q*, gpm 1691 3374 5147 6854 10211 13614 2368 4805 7212 9635 14375 19166
____________________________________________________________________________
* Discharge or flow rate, gallons per minute (gpm)
SALT BUILDUP
Many lagoon liquid recycling systems have experienced a buildup of a grayish-white crystalline salt
on the internal pumping and pipe surfaces. This compound is predominantly magnesium ammonium
phosphate sometimes referred to as struvite. Predicting the occurrence of salt crystallization is very
difficult since exact causes and remedies for the deposition are not well defined. The following
design, maintenance and management techniques help in many cases to minimize the buildup.
Piping System Use nonmetallic pipe and fittings. Polyvinyl chloride (PVC,white), polyethylene (PE,
black), and acrylonitrile- butadiene-styrene (ABS,black) are typical pipe materials being utilized. The
black PE and ABS pipes are reported to give slightly less salt troubles than the PVC. The minimum
pressure rating of recharge pipes should be 80 psi. Consult with pump experts to size pipe diameters
large enough to maintain flow velocities between 3-5 feet per second. The minimum pipe diameter at
any point in the system should be 1.5 inches. Table 7 gives flow capacities for various PVC Class 125
sizes to keep the flow velocity between 3-5 feet per second. Minimize sharp bends such as elbows and
tees with rolled PE pipe and long sweep elbows for direction changes. Piping systems not in
continuous use should be planned for draining between pumping events.
Electrostatic Charges Direct grounding of the pump housing helps to discharge any static charges or
stray voltage believed to contribute to salt deposition. A metal ground rod should be driven 10-12 feet
into moist soil near the lagoon edge. Check cable edge. Check cable connections at the ground rod and
pump periodically for corrosion.
Table 7. Maximum Flow Rate for Class 125 PVC Pipe
__________________________________
Nominal pipe
Flow velocity, fps
diameter, in
3
5
__________________________________
-------gpm--------1.5
25
40
2
37
60
2.5
55
90
3
80
130
4
130
220
6
285
475
__________________________________
Lagoon Treatment Primary lagoons should be properly sized with adequate treatment capacities to
minimize salt buildup potential and to achieve odor control and a lagoon liquid suitable for flush
recycling. Current recommendations are 1.5 cubic feet of liquid volume per pound of live animal
weight as primary treatment plus another 0.5 cubic feet per pound as storage either in the primary
lagoon or a second-stage lagoon. New lagoons should be charged at least half full of water prior to
startup and the liquid level brought up to design levels as soon thereafter as possible. Rainfall during
normal years dilutes lagoon liquid concentrations while extended periods of hot, dry weather increase
nutrient and salt levels and the rate of salt buildup in recycling systems. During these periods, flushing
with fresh water or irrigating a portion of the lagoon contents replaced by fresh water may be
advisable.
Acid Cleaning Salts can be dissolved from internal pump and pipe surfaces with dilute acid
treatments. Removal of heavy buildups require several dosings followed by flushing of the acid and
dissolved salt solutions or an acid recirculation loop. A recirculation loop consists of an acid-resistant
reservoir tank with capacity to supply enough solution to fill the pipe length to be cleaned as
determined from Table 8 plus some reserve to keep the pump primed. The flush pump suction is
switched from the lagoon and connected to the bottom of the acid tank with a quick-connect coupling.
A 1-inch line from the end of each pipe section treated returns acid to the tank.
Muriatic (hydrochloric) acid (30% (20o) technical grade) is diluted (one gallon acid added to 9 gallons
water). Extreme caution must be exercised since mixing of acids with water can be very hazardous.
Never try to add water to the concentrated acid. Always partially fill the tank with water, then add the
acid to the water very slowly. Heat will be generated. Eye protection is advisable. Recirculations
ranging from two hours to overnight will be required depending on the degree of salt buildup. This
dilution should not hurt metal although prolonged contact should be avoided. A heavy buildup may
render the acid usable only one time; although it should be retained after the first use and reused to see
how much strength remains. Spent acid may be dumped to the lagoon.
Table 8. Class 125 PVC Pipe Volumes
_____________________________
Nomimal pipe
Gallons per
diameter, in
foot of length
_____________________________
1.0
0.06
1.5
0.13
2.0
0.20
2.5
0.30
3.0
0.44
4.0
0.73
6.0
1.58
_____________________________
FLUSH FREQUENCY
High density housing units such as finishing buildings, grower units, and caged nurseries should be
flushed as least 4 times daily for adequate solids removal and odor control. This frequency requires
automated flushing equipment. Farrowing houses and flat deck nurseries might be flushed less
frequently to conserve heat in the winter since the waste quantities produced in these houses are
greatly reduced. A standpipe drain (figure 7) would allow pit recharging with the option of storing
waste as long as a week between flushes. This management mode provides a similar degree of gas and
odor control as more frequent flushings. Both options greatly improve in- house conditions when
compared to prolonged pit storage of manure.
PIT CONSTRUCTION
A pit depth of 24 in below the slats or deck is recommended to separate the manure and urine on the
pit floor between flushes from the animal's breathing zone and to allow the underfloor ventilation
system to remove the gases. Pit dividers as shown in Figures 6 and 9 are necessary for wide pits to
channel the flush water and prevent meandering around heavy waste accumulations. Flush channels
no wider than 4 ft have given the best performance. Animals on slats were observed to establish
dunging habits along the edge of pens resulting in heavy waste accumulations in outside channels
rather than uniform distribution of manure across the entire pit width. This would either suggest
making those channels with the heavier waste buildups narrower, distributing more water to them,
and/or flushing more frequently.
DRAIN CONSTRUCTION
The flushed waste must be collected and removed from the building such that flow is not restricted.
Inadequate drain capacities leave undesirable solids deposition at the lower end of the flush channels.
A cross gutter inside the building across the end of the flush channels 16 in wide and sloping from 4
to 8 in below the pit floor conveys the flushed waste to a collection box on one side of the building
(figures 8 and 9). Drain pipes must be large enough to handle the discharge rate from the gutter. An 8in diameter pipe is the smallest drain recommended for wastewater transport. The entire cross
sectional area of the drain pipe should be below the collection gutter to ensure that the pipe flows full
(figure 10). Table 9 gives flow capacities for various size drainpipes at different slopes. Drain pipes
should extend into the lagoon at least to the toe of the bank slope. For better odor control, a turn-down
collar at the end of the drain pipe for discharge below the liquid surface is preferred.
Table 9. Flow Capacities of Round Sewer Drainpipe
_______________________________________________
Nominal
Slope of Pipe, %
Drainpipe ____________________________________
Diameter
0.1
0.5
1.0
1.5
2.0
_______________________________________________
inches
--------gallons per minute-------2
4
9
13
16
19
3
12
28
40
48
56
4
27
60
85
105
121
6
80
179
253
309
357
8
172
385
544
666
769
10
312
697
986
1210
1390
12
507
1130
1600
1960
2270
14
765
1710
2420
2960
3420
15
919
2060
2910
3560
4110
16
1092
2440
3450
4230
4880
18
1490
3340
4730
5790
6690
20
1980
4420
6260
7660
8850
22
2550
5700
8070
9880
11400
24
3220
7200
10200
12500
14400
_______________________________________________
SUMMARY AND CONCLUSIONS
Basic hydraulic relationships were used in conjunction with a laboratory developed empirical
relationship between manure viscosity and dry matter content to develop predictive data and design
criteria for planning swine waste flushing systems. Field verification of these recommendations has
resulted in widespread implementation of flushing systems in North Carolina which are responsive to
the needs of large as well as small operators.
Specific conclusions are:
Flushing systems are not a substitute for ventilation.
Flush system discharge rates must sustain a 3 fps flow velocity for adequate manure removal.
Recommended minimum flush tank volumes range from 1.4 - 1.6 gals/100- lb hog.
Recommended minimum flush frequencies for finishing buildings are 4 times per day.
High-volume pump systems should deliver between 80 - 100 gpm per foot of flush channel
width.
Drain systems should have enough capacity to prevent flow restrictions.
REFERENCE
Barker, J.C. and L.B. Driggers. 1980. Design criteria for alternative swine waste flushing systems.
Livestock Waste: A Renewable Resource, Proc 4th International Symposium on Livestock Wastes,
American Society of Agricultural Engineers, St. Joseph, MI. pp. 367-370, 374.
Not Included:
Figure 2. Small-diameter single siphon flush tank
Figure 3. Large-diameter multiple siphon flush tank
Figure 4. Free-swinging flush bucket (Univ. of Tenn. Plan No. T4044)
Figure 5. Ground level flush tank with water weighted valve opener
Figure 6. High-volume flush pump distribution header
Figure 5a. Beginning of fill cycle. Tank empty; valve closed; 2-3" slack in valve chain; reservoir empty.
Figure 5c. Just prior to valve opening. Tank full; valve closed; valve chain taut; water rapidly filling reservoir.
Figure 5e. Just prior to valve closing. Tank empty. When all water drains from reservoir, valve closes, valve
chain becomes slack, and fill cycle begins.
Figure 5b. Water beginning to enter reservoir. Tank nearly full; valve closed; 2-3" slack in valve chain; some
water in reservoir.
Figure 5d. Valve fully open. Tank emptying; valve open; valve chain taut; reservoir about 2/3 full of water.
Figure 7. Pit drain standpipe valve
Figure 8. Waste collection box
Figure 9. Pit drain collection gutter
Figure 10. Drainpipe connection
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and
program opportunities are offered to all people regardless of race, color, national origin, sex, age, or
disability. North Carolina State University, North Carolina A&T State University, U.S. Department of
Agriculture, and local governments cooperating.
EBAE 080-81
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