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Waste Holding Tanks


Some Design Guidelines

1. Try to arrange the bottom of the tank to slope towards the suction outlet pipe.
2. Try to position the inlet so that solids do not need to migrate across the bottom of the tank.
3. Vent the tank with a minimum of 1/2″ bore non-collapsible hose. Avoid water traps in the vent line.
4. Try to avoid long pipe runs.
5. Empty tank before it is full so that solids do not enter the vent pipe.How Big?If sink and shower waste are also being contained then the holding tank must be substantially larger. Used with care, a shower will require about 12 litres each time it is used. Obviously both sink and shower waste quantities depend entirely on how the facilities are used, as well as frequency of use. The size of a holding tank is entirely dependent on the berth/size of the boat and the anticipated duration between pump-outs. A holding tank can never be too large; but can be inconveniently small. Restriction on size depends on available space for installation and effect on the boat’s trim. The following formula will provide an approximate guide to the minimum size of the tank which is acceptable:Berths x days between pump-out x Y = Litres capacity of tankFor recirculating systems factor Y = 2
For fresh water flush systems Y = 10The above assumes low-water-use toilets are being used and does not allow for sink or shower.Dr. Yusuf Civelekoglu, CMI
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