Holding Tank - Becomes Pressurized

[MoodySabre]

As you have had trouble from the outset there is nothing proven to be correct.

1. Is the outlet pump in the right way round? Pumping water in through this would be at greater volume than could be released by the smaller vent pipe and that could pessure when pumping. This may also have filled the vent pipe with water as mentioned above.

2. Is the dark blue/light blue item the filter? Have you taken it apart to check it is clear?

3. Is the seacock opening properly?

4. You said it was a tight vertical fit - does that mean you can't take the inspection cover off without some risk (eek).

I like the suggestion that the vent has been attached to the outlet by mistake and therefore doesn't vent. Similarly the pump wouldn't removed anything from the tank if it attached to a connector without a dip-pipe.

 

[Jokani]

Looks like it's almost certain that your tank will be wholly/mainly below sea level, so water will flow in through the outlet pipe. The outlet pipe needs to loop up some way above sea level, then back down to the outlet, with an anti-syphon device at the highest point.

Arggh! I hope not, I thought that the pump was one way so I had not considered that water could enter via the outlet pipe - I can get the pipe maybe and inch or two higher any more and I'll struggle. I would need to take the outlet in to the toiler area and back in to the locker a round trip of maybe a couple of metres.

I may fit a level gauge (would be good long term) to confirm that water is entering via the outlet - or I could remove the blanked off fitting to visually confirm I guess.

If you are right, I may even need to consider moving the tank to a locker in the fore-cabin, which is above the waterline. I did not choose this option before all the pipes would be a lot longer.

Thanks for your help, Gary.

 

[Jokani]

The sagging vent pipe looks like the main culprit to me, especially with the charcoal cartridge in it. Bit of soggy loo-roll shoved into the front of the filter and blockage seems almost certain.

Also the pump is mounted upside-down. Maybe you have no other option and have to accept it, but Whale's instructions say that the motor should be above the pump chamber in case of leaks.

Pete

I'll check the pipe, and refit so that it does not sag, I'll probably reposition the filter to somewhere more accessible while am at it.

Thanks for your help, Gary.

 

[Tranona]

The filter should not really be necessary. Aim to route the vent pipe to go vertically above the heeled water line as soon as possible out of the tank. Pretty sure the inlet just goes straight in and the outlet has a stack pipe, so might be worth taking the plate off and checking you definitely have them connected correctly. Assume you have the pump mounted in the correct direction. You should not need a vented loop downstream from the tank - in fact it is a bad idea as you want the shortest possible run to the seacock. It does not matter if seawater gets back in as the loop between the tank and the loo will take care of it. Think of the tank as just a large extension (in volume) to the pipe and is itself vented by the tank vent so never under any pressure. Think you will find the little brass plug is for fitting a level sensor.

 

[Forty_Two]

I'll check the pipe, and refit so that it does not sag, I'll probably reposition the filter to somewhere more accessible while am at it.

Thanks for your help, Gary.

Keep the vent filter above the tank, they do not like being wet & you sure won't like changing it when wet. You really must avoid getting effluent in the vent pipe & filter or it's not going to do it's job.

 

[nigelmercier]

You should have a one inch pipe from the vent fitting to a skin fitting (without any obstruction or valve) fitted high above the water line...

And in my case, pointing at the boat in the adjoining berth

 

[PCUK]

Sorry but the only plausible explanation to me is that you have the connections wrong, perhaps the vent is connected to the outlet, and as this has a dip pipe to the bottom of the tank it would not vent, it would perhaps also prevent the tank emptying.
I assume you are emptying the tank by opening the seacock when at sea to bottom drain the tank.
Otherwise something is very blocked.

That sounds like a very plausible suggestion!

 

[blackbeard]

Just a thought - you mentioned testing the installation with water and loo paper.

Normally, loo paper will be shredded by the action of the pump which is integral to the loo, so that whole sheets don't get into the holding tank. Also, there is loo paper and loo paper - the type which rapidly disintegrates in water (expensively designed to do this, or else supermarket cheapest) and the luxury kind-to-bum type which doesn't. The latter will probably succeed in causing a blockage somewhere (as will kitchen roll, hand wipes and baby tissues).
So it's possible that your loo paper test might have introduced a blockage, possibly in the air vent as already mentioned. If it exits the boat still recognisable as loo paper, this is not a good sign.
Anyway, that vent is your prime suspect although there could be other (t)issues involved.

 

[Jokani]

That sounds like a very plausible suggestion!

Looking at the diagram supplied by the manufacturer and the photo of my installation the three connections are all connected to the correct pipes. The vent would be hard to connect incorrectly as it is a considerably smaller diameter that the in and out connections. Once I have rectified all other issues, if I still have a problem than as a last resort I guess I will have to remove all the fittings to confirm which fitting/s have a dip pipe.

 

[nigelmercier]

If any liquid gets into that filter, it will clog very quickly. Remove it and see if it helps.

 

[pmagowan]

Well the problem with the pressure is the vent pipe. You have all the connections correct but the vent pipe has a filter blocking it and is below the level of the tank. It is likely that this is wet and blocked. There is no other way to pressurise the tank as even if the pump was working backwards the vent would equalise the pressure (more or less) despite its smaller size. It would have to be a bloody powerful pump to pressurise a tank with a ruddy big hole in it. You had a presurised tank therefor the ruddy big hole is not working therefore it is blocked and the prime candidate is that ruddy filter!