Fitting a holding tank

Cspirit

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I would like to hear the Forum's views my proposed holding tank set up. I have fitted HTs to two previous boats but this one (an LM27) is around half the size of the last boat and, of course room is very tight. I only need and can only fit a small tank - about 28 litres - but I sail alone and I think that this will suit my needs. I'm not proposing to fit a pump out facility. I have fitted a new Jabsco toilet - ideally I would have a Lavac but replacing like with like was simpler. There are two ball valves on the inlet and on the outlet to the toilet as a precaution. I propose a small HT below the waterline with a Jabsco three way valve enabling choice - to tank or sea. The outlet from the HT goes via a macerator pump and then to a seacock below the waterline.

I know that this discharge below the W/L is not recommended but it seemed to work in the two previous installations. However, in those two, the HT was above the W/L. So, given that I won't be using the HT much and I can easily access the seacock plus I'm thinking of fitting a Trudesign NR valve between the pump and the seacock - what does the team think?.

Thanks in advance, Bob

Retreats and dons tin hat.
 

BabaYaga

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I have a HT installation, somewhat similar to what you propose, which works well.
A few points:
Having installed HTs twice you are probably aware of the need for at vent hose to the tank. Mine is 19mm ID taken from the top of the tank to a skin fitting high up on the hull side and I have found the size adequate.
Instead of a three way valve you might be able to use a t-piece + an additional ball valve added to the existing outlet ball valve.
Not sure what the NR valve does. Is this a back up for if you forget to close the tank discharge ball valve after operating the pump?
I am not aware of any drawback of having this ball valve/seacock below the WL, but then I use a manual diaphragm pump for discharge (which has two NR valves incorporated).
If you would like to add a pump out facility at a later stage, this can be arranged by taking the hose from the deck fitting to a t-piece in the hose section between the tank outlet and the macerator pump.
 

Cspirit

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Thanks! Yes, I will be fitting a vent. The reasoning behind the NR valve at that point is exactly as you state. In case I forget or can't be bothered when sailing to close the seacock!
 

MoodySabre

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I put in a Y connector so the macerator outlet connects to the toilet out hose. Saves another hole in the hull. Works fine. Otherwise my set up is as yours but no nonreturn valve. I do have a deck pump out which I would not want to be without.
 

rogerthebodger

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I have a very similar arrangement to what you propose

the only comment I would make is to ru the outlet pipe from the pump out pump up to the underside of the side deck then down to the seacock pump out exit.

I would also do the same for the head outlet to stop any back flow

pipework up under side deck


3 way valve at bottom of picture


WT pump out pump


All inlets and outlets on top of tank to reduce back flow
 

Cspirit

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Many thanks everyone - that is really helpful. My particular problem is space, or rather, lack if it. The LM27 is a lovely little boat but everything is very tight!. The only place for the HT is small and below the water line. Moreover, the base of the tank is below the site of the exit seacock so my concern is that when the discharge seacock is open the tank could fill with seawater thus reducing its capacity. For this reason I'm considering the NR valve. I'm aware that they have a reputation for getting clogged but feedback on the Trudesign version seems to be good.I agree with Roger that it would be good to run the outlet pipe from the macerator pump up to the decking back - I have done this on the head outlet but unfortunately it's simply not possible on this boat, hence the proposal to fit a NR valve.

Thanks to MoodySabre for the suggestion to use the existing toilet outlet seacock. I dd this in the last boat with no problems. I'm not sure why I didn't consider this with the present installation!

Finally - deck pump out. In nearly 20 years in the Med I only had two shoreside pump outs, both in Turkey, so you can see that it's not a priority for me yet. Perhaps I'll fit one in a year or two....

I think I'm getting there - thanks for all your useful comments.

Bob
 

billyfish

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I too have very little space on a Degero28 when I got her 3 years ago. The heads outlet went straight to the holding tank then a separate manual pumps it outboard. A tee peace at the bottom of the tank also goes to pump out. It stank. So I thought I would be clever and put it a three way valve with non return valves so I could discharge straight outboard or to the tank , that stank as well. This is after removing and cleaning the tank and replacing all pipework...moving on I have now returned it to the original setup as there is much less pipe for it to 'dwell in' and the pipe can be changed easily and often. The smell was mostly coming from the vented loop. The water line is about 6" below the top of the tank and the top of the pipes, hopefully enough to stop back syphon, the only vent goes from the top of the tank outboard. The whole lot is under the fore cabin bunks as , I believe, factory fitted. So far so good but only used it once. Just have to keep flushing the tank out.
 

Stemar

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I don't know how it would work, never having used a holding tank, but I have heard it suggested that it's useful to have the deck emptier, the tank and the sea outlet in a straight line so a rod can be used if you get a blockage
 

Tranona

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I don't know how it would work, never having used a holding tank, but I have heard it suggested that it's useful to have the deck emptier, the tank and the sea outlet in a straight line so a rod can be used if you get a blockage
That is correct. The two systems that I have installed were designed to do this, and on one actually used in anger. However this only works with gravity tanks and the ones under discussion here are below waterline pumped systems.
 
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