Advice please on holding tank installation.

[AndrewB]

There is a holding tank fitted to the yacht I have just bought, with a pump on the outlet line so it can be emptied overboard through the hull.

I want to add a pump-out deck fitting, as an alternative method of emptying in marinas that have pump-outs.

My question is, should the diverter valve be fitted before or after the pump?

In other words, do marina pump-outs actively suck out the holding tank contents, or do I need to do the pumping?

 

[johnphilip]

Shoreside pump outs have a huge, yes huge suction so that when they connect to your tank the contents fly up the dip tube and off to the storage. The important think to check is that there is an adequate vent to allow air back into the tank to prevent it imploding. Tec Tanks and others show a vent as large as the pumpout pipe but the tank I bought and fitted had only a 3/4 inch vent connection so I hope this proves adequate if ever I get a deck fitting and use it.

 

[pvb]

In other words, do marina pump-outs actively suck out the holding tank contents, or do I need to do the pumping?

Marina pumpouts suck, so your diverter needs to be before the pump. Ideally, you could just have a dedicated 1.5" suction pickup for pumpout, this obviously needs to go to the bottom of the tank. Because the suction is considerable, the vent pipe should also be 1.5" and you also need a 3/4" rinse fitting. There's some good advice and useful pics in Leesan's guide - see http://www.leesan.com/uploaded_files/datasheets/leesystem tank fitting instructions.pdf

 

[Cloven]

Diagram below of the system I have on my boat may help. My air vent pipe is the same size as all the other pipework.

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[AndrewB]

Marina pumpouts suck, so your diverter needs to be before the pump. Ideally, you could just have a dedicated 1.5" suction pickup for pumpout, this obviously needs to go to the bottom of the tank. Because the suction is considerable, the vent pipe should also be 1.5" and you also need a 3/4" rinse fitting. There's some good advice and useful pics in Leesan's guide - see http://www.leesan.com/uploaded_files/datasheets/leesystem tank fitting instructions.pdf

Thanks for that: I was confused by the advice given with my old Lavac instructions (my new boat has a Blakes though), as shown in the diagram below.

I'm not sure why a separate rinse fitting is needed. I just flushed mine out from the WC, though admittedly it took a lot of pumping. Does it also provide the additional venting that Johnphilip says is needed? A small air-vent is already fitted to mine, but not 3/4".

 

[pvb]

I'm not sure why a separate rinse fitting is needed. I just flushed mine out from the WC, though admittedly it took a lot of pumping. Does it also provide the additional venting that Johnphilip says is needed? A small air-vent is already fitted to mine, but not 3/4".

The separate rinse fitting allows the marina pumpout operator to rinse the tank quickly. The vent really needs to be the same size as the pumpout pipe, otherwise you run the risk of damaging the tank. For the sake of a few quid, it's surely worth avoiding tank damage.

 

[NPMR]

The separate rinse fitting allows the marina pumpout operator to rinse the tank quickly. The vent really needs to be the same size as the pumpout pipe, otherwise you run the risk of damaging the tank. For the sake of a few quid, it's surely worth avoiding tank damage.

We simply use the pump out hole to refill the tank from a hose and then either pump out again or let the fresh water run out of the bottom of the tank depending upon how clean/clear it is.

We have had blockages (this is our first year of a holding tank) and had problems because of previous owner, I suspect, not flushing through very often, if at all. No problems since we started flushing regularly and used more strokes of the heads pump than before. So we had a higher ratio of 'flush' to contents.

 

[Cloven]

We simply use the pump out hole to refill the tank from a hose and then either pump out again or let the fresh water run out of the bottom of the tank depending upon how clean/clear it is.

Quite agree - we use the vent hole which means we can still leave the pump out connected. This of course assumes you have a vent pipe big enough for hose access.

 

[macd]

Two points worth making:
1. air is a deal less viscous than sewage, so the vent need not be as large as the pump-out. However, an over-generous air vent is no bad thing in precluding anaerobic bacterial activity in the tank, which is what causes the worst pongs. 3/4 inch with a long, convoluted run is probably way too small.

2. Some marinas (out here, at least) have pump-out machinery with no dip-tube: they depend on the pump-out fitting having its own tube to almost the bottom of the tank. I watched in amusement as one marina's crew applied their shiny, brand-new pump to my deck fitting. Even after showing them diagrams, they couldn't work out why it didn't work, but simply drew in air from the vent.