Lavac and Holding tank considerations

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ean_p

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thinking of installing a Lavac toilet and fitting a holding tank close alongside. The tank will be mounted above the outlet valve on the skin fitting so as to drain straight through, so the bottom of the tank is about level with the top of the toilet. The tank then will be relatively tall/ vertical in shape at about 31/2 - 4 ft tall. As the hose from the toilet has to discharge into the top of the tank what will be the effect of that longish run (approx 5ft+)of hose on ;
a/ the residual level of water in the loo bowl? and
b/ the quantity of water going into the tank on each 'usage' cycle
I would envisage that the pump would be mounted inline some where along the hose and if any of these have a negative effect then what might be done to minimise or overcome them please?
 
I have a similar set up. Not quite so long. No effect on the water coming into the bowl as this is a function of the vacuum when you stop pumping (and the size of the hole in the inlet relief valve). Clearly you need to pump enough to clear everything into the tank, but the normal cycle seems to do that OK.
 
does not the water remaining in the pipe above and below the pump drain back down into the bowl over time (I assume that the pipe is 'full' of water after the required nominal 10 flushing strokes or what ever) and so add to that already there, or conversely if it doesn't drain down but sits in the pipe then it would add to that amount going into the tank at the beginning of the flush cycle and thereby almost double the amount deposited ( sorry about that !) in the tank during one flush cycle. Or is the assumption of a full pipe wrong? I haven't fitted the Lavac yet so aren't fully 'au fait' with it's workings
 
The water in the pipe between the bowl and the pump does not tend to drain back into the bowl. Air would have to enter the pipe for that to happen. The only way in for air is at the bottom, ie the outlet from the bowl and you would normally leave enough water in the bowl to cover that. If you don't then yes some water can drain back but only until the outlet is covered.

Different of course if the pump valves let by then all the water above the pump as well could drain back. However, when that happens it is time to service the pump!
 
If I remember rightly the pump has a joker valve on the outlet. I have never had any problem with leakage, but it is only 2 years old and not used much.

Incidentally on my other boat which has a Jabsco, the entry to the holding tank is at the bottom with an internal stand pipe to exit just under the top. This was because there is not enough room to take the pipe to the top and get the tank high enough to gravity drain. Seems to work OK. If you had room to do this, as in space to fit the pump and operate the handle, it might make for a shorter pipe run. Can't think of any reason why it would not work. Definitely looks neater if the pipework is exposed.
 
Sounds workable. The Lavac pump has to be above the bowl. After flushing with the lid down, wait 30 seconds and lift the lid, then pump until the bowl is dry. Over time some water may drain back but a few extra pumps with the lid open seems to evacuate the hose of water as the pump forces it into the tank with air.
 
AMAOI, can anyone tell me how roughly much effluent is produced by a single use of a Lavac toilet ?

Thanks,

Boo2
 
While I haven't measured Lavac suggests less than a conventional head as the pump is much more efficient. A big advantage is that a Lavac will virtually never get plugged.
 
The shorter the pipe run the better if you want the Lavac to work at its best and have fewer pumps to empty the bowl and establish the vacuum. There is also less risk of getting a pipe sag and consequent pool of liquid in the pipe, leading to nasty niffs .

On the face of it the scheme sounds feasible but it may we worth considering building in the possibility to pump out the tank ( from a shoreside pump) where you may be in a situation where you cannot drain to the sea. In which case you have to be sure that your tank is sufficiently robust to resist imploding under the suction pressure and also thet you have a sufficiently large vent pipe (38mm). In any case, if the vent is too small you risk getting bad smells because the anerobic activity in the tank content is inhibited.

I can recommend Tek Tanks for supply of tanks, especially custom jobs to fit tight spaces.
 
Vacuum is created with the first stroke as long as the lid is closed as it pulls the intake water through the bowl. A good size for the vent is 1' (25mm). Best to have 2 vents for less smell and more airflow.
 
My experience of Lavac suggests that they are unhelpful, disinterested in customers and wanted £69.55 from me +VAT for a 3" 90 degree hinge bolt.

I will be disposing of mine at the next service interval.
 
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