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Waste tank design


Duck-n-Dive
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This is not a fashion question.

Plastic waste tanks I have seen have a dip pipe for the "extraction" with a connection on the top of the tank.  I have seen a couple of stainless tanks, where the pump out connection is simply a connection off the side of the tank at the bottom.

Does any body know which is better, or is it just a preference?

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I have built stainless tanks before and I'll assume the plastic tanks are injection moulded.   My guess its easier to make plastic tanks with internal pump out connection. Ref the stainless tank, building wise it wouldn't make much difference. I'd say its down to the space you want to fit it in...

Edited by Quattrodave
typo
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3 minutes ago, Quattrodave said:

I have built stainless tanks before and I'll assume the plastic tanks are injection moulded.   My guess its easier to make plastic tanks with internal pump out connection. Ref the stainless tank, building wise it wouldn't make much difference. I'd say its down to the space you want to fit it in...

Big plastic tanks are blow moulded.  If you are going to make a hole in a plastic tank and you don’t want a weeping leak, then put it in the top so it is above the liquid level.  With a steel tank it is usually easier to make a reliable seal, so can be low down.

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14 minutes ago, Robbo said:

Always go from the top, sanitation hoses will smell if they hold any waste in them.

 

I was wondering if there was a problem with the outlets holding waste, but I was thinking about stuff solidifying in the pipe. I thought proper sanitation hose wouldn't let smells through.

I am torn between the two at the moment. Stainless is cheaper (surprisingly) and according to some people it will last longer, however the plastic tank I  looking at doesn't need side support, and you can see the level in a plastic tank by shining a light through it, just in case the level gauge fails.

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4 minutes ago, Duck-n-Dive said:

. I thought proper sanitation hose wouldn't let smells through.

Even the expensive stuff does eventually, you'll see instructions on not to have it installed where it holds any waste, you are also meant to replace it every 5 years so recommend using rigid pipe where you can.    Even if it didn't eventually smell, if you ever needed to replace the hose for any reason, having not to empty the tank totally can only be a good thing.

 

Edited by Robbo
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1 hour ago, Robbo said:

Even the expensive stuff does eventually, you'll see instructions on not to have it installed where it holds any waste, you are also meant to replace it every 5 years so recommend using rigid pipe where you can.   

 

 

I fitted about 2.5m of Vetus flexible barrier sanitary hose between my vacuflush toilet and cassette docking station more then 15 years ago and it still hasn't let any smells through. I think mine is about 40mm ID from memory. Since I only empty the cassette, the waste pipe itself has been full of waste since it was installed. Perhaps I've just been lucky but the toilet has been in full liveaboard use all that time.

 

The Vacuflush installation instructions didn't require the pipe to be installed so that it didn't stay full of waste and I'm pretty sure the Vetus instructions didn't say anything about that either and I did read all their instructions. Also do you have a reference to the 5 year replacement? I wasn't aware of that either - perhaps you're talking about a different make of hose as I can't find anything in the Vetus specs about a 5 year lifespan for their sanitary hose.

 

What Vetus did say was that bending a flexible barrier sanitary hose below a certain radius could cause the barrier layer in the pipe to rupture and would invalidate the warranty.  

 

Out of interest, According to Leesan the way to determine whether a barrier pipe is allowing smells through, or whether the smell is coming from elsewhere, is to wipe the pipe with a damp cloth and then smell the cloth outside or away from the installation. About 10 years ago I thought the pipe was responsible for smells in the bathroom, but I did the test several times and it wasn't the pipe. In the end it turned out to be smells from the outside vent blowing back in through an open window!

Edited by blackrose
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1 hour ago, BEngo said:

Lot easier to rod a side connection than a dip pipe, should it be required.

N

Is it, surly it would terminate with a 90 deg bend

Mine has a dip pipe and its a straight run from the deck fitting to the end of the pipe 15mm or so above the bottom of the tank, so if needed easy to rod right through. When I was on the Gt Ouse I use to shove the big bore flush pipe down and give it a blast out.

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