Lavac holding tank layout & installation advice please

" Although I wasn't aware of this solution, now that you've mentioned it, I can see the sense in a gravity holding tank. The only way I could see that fitting is to have it situated in the tall thin cupboard in the fore cabin where I had envisage the pipe loop, however I guess I could also explore using the space occupied by the small cupboard inside the heads compartment. That's not visible in my diagram, but it's essentially just above the photographic section. Thanks also to you (and Chris_Robb) for advice on keeping the hose lengths as short as possible. That's something I'll keep in mind when deciding where to put things. Thanks for your help."


I read a paper on my Owners Club website where this has been done. The tank is in use all the time and black water flows through it. In confined waters the gravity cock is closed and the tank fills, till the opportunity comes to empty it.
It is a small space, above the heads, but the author thinks he may have enough room for three days use on a lightly crewed boat. The advantages are it takes away no storage space and is totally unobtrusive.
 
doug748 said:
I read a paper on my Owners Club website where this has been done. The tank is in use all the time and black water flows through it. In confined waters the gravity cock is closed and the tank fills, till the opportunity comes to empty it.
It is a small space, above the heads, but the author thinks he may have enough room for three days use on a lightly crewed boat. The advantages are it takes away no storage space and is totally unobtrusive.
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This arrangement is pretty standard on new boats and one of the benefits of wide after sections of the hull. high freeboard and aft loos. You would not notice where the tank is on my boat even though it is 60l capacity. However, much more difficult to find space on existing boats with narrower beam and lower freeboard which means little space available around the loo. So most systems in older boats are pumped types with the tank in an underberth locker as on Tillergirl.
 
macd: Thanks. I hope that you enjoyed the big day!

Hugh Foulis & pvb: Alas, lakesailoring is before my time. Probably just as well ;)

doug748 & Tranona: I'm now seriously considering this. I reckon that there might be enough room to cram everything into the tall thin cupboard in the fore cabin. We won't need a large black water tank, so it might just fit. Of course, I'd need to create a large access hatch (in the fore cabin) through the cupboard. Thank you.

One thing that I'm a little unsure about is using the Lavac when the tide is out (most of the time where we cruise) if I drop the fresh water in option. How does the Lavac cope if the pump is sucking on air?
 
Surely you will want a diverter valve to select the fresh water tank for flushing. Dead easy if you have the space. But the pump will suck the bowl empty. Interest though how well it will vacant the contents into the holding tank without any flushing. I think I would be requiring sufficient fresh water to do this.
 
I'm going to raise my head above the parapet and offer a :encouragement: for fresh water flushing. It definitely results in a slightly less whiffy loo experience

However, it isn't so much of a benefit that I'd fit it purely for that reason

But am I right in getting the impression that you're on a drying mooring? If so you'll find that whilst the pump will empty the bowl of liquids without an incoming water flow, it won't clear the waste pipe entirely no matter how much you pump (or, to be strictly accurate, it won't on our setup) and when the tide comes in it pushes the un-expelled waste back into the toilet bowl

Of course, this won't be a problem with a holding tank, only with a direct overboard system (and of course that can only be used for, ahem, liquid waste)

If you are on a drying mooring I would fit a fresh water flush facility but I wouldn't have that as the sole source of flush water, I'd still want a seawater flush connection with a change over valve
 
We have a pull out spray head on out aft head that can reach the bowl of out Lavac so we can just position the spray over the bowl to fill with fresh water of clean the bowl when needed. This can also be used to provide flush water if the boat is ever aground.
 
yodave said:
One thing that I'm a little unsure about is using the Lavac when the tide is out (most of the time where we cruise) if I drop the fresh water in option. How does the Lavac cope if the pump is sucking on air?
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Isn't it marvellous how these important little facts are so frequently omitted from the original questions? If you'd put this information in the OP, you'd have got a different set of answers.
 
pvb said:
Isn't it marvellous how these important little facts are so frequently omitted from the original questions? If you'd put this information in the OP, you'd have got a different set of answers.
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Agree. If the need to use the loo when not afloat is important, then fresh water flush is key. Rogershaw's solution is OK but not ideal with a Lavac as the mechanism to evacuate also creates a vacuum to draw in water to the bowl.

Having a fresh water option using a Y valve on the inlet is viable, but suggest an independent freshwater tank of a capacity at least equal to the holding tank would be needed, rather than drawing from the drinking water supply. Whether this additional complication is worth it only the OP can decide.
 
Tranona said:
Rogershaw's solution is OK but not ideal with a Lavac as the mechanism to evacuate also creates a vacuum to draw in water to the bowl.
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True up to a point as running fresh water from the sink tap with pressure feed directly into the bowl with the lid open does not need and vacuum to draw water in . Also a spray can clear and part of the bowl that the vacuum flush does not reach if you have an explosive discharge into the bowl.
 
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