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Pump Out Holding Tank


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Hello,

 

Can these types of tanks be used for holding pump out waste? (Obviously in the black version) Or does it need to be some kind of special plastic? As these seem much cheaper.

https://www.tanks-direct.co.uk/water-tanks/water-storage-tanks/600-litre-water-tanks/650-litre-water-tank-flat-baffled.html

Regards

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A holding tank failure is a bad thing to happen so do you want to risk it?

Possible issues might be.....

wrong sort of plastic (you should be able to check this).

not as strong as a proper pump out tank, especially if its a dump through where the bog sits on top

baffling arrangement not suitable to allow good draining of sludgy waste

a proper tank should come with a suitable suction outlet welded in and set at the correct height, this one won't, you will have to sort that out.

..........Dave

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Be warned, many plastics are permeable to nasty niffs from inside the tank.

Nothing would induce me to have a plastic toilet tank. I would only have minimal lengths of flexible pipe on the system, none where effluent can lie in it.

6mm welded steel or a stainless tank for me.

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45 minutes ago, mross said:

If getting one built, I would go for a sloping bottom.  Plus a recess/sump.  The aim being to get the tank as empty as possible on a pump out.  Also, fit a good hatch on top for cleaning out.

The tank sits on the floor of the boat so a sump is not easy to do, though I suppose it could protrude into a hole in the floor between any crossmembers. Good pumpout practice is to rinse the tank and rock the boat so I am not sure that a sump would be a big improvement.

The inspection hatch, when fitted, is only to deal with blockages, with good pump out practice the tank should never need cleaning, and its not a job to do just for the sake of doing it.:D

.............Dave

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1 hour ago, Tony Brooks said:

Be warned, many plastics are permeable to nasty niffs from inside the tank.

Nothing would induce me to have a plastic toilet tank. I would only have minimal lengths of flexible pipe on the system, none where effluent can lie in it.

6mm welded steel or a stainless tank for me.

There are many many instances of mild steel tanks rusting through, just do a forum search!. The story that urine pickles the steel so that its lasts forever appears to be a myth.

There are many instances of stainless water tanks splitting along the welds though I have not heard of a stainless poo tank splitting.

Almost all modern poo tanks are plastic and I have not heard of any significant failures. I think a forum thread reported a failure around a hose fitting weld probably due to a bad installation causing stress. I suppose as plastic tanks are relatively recent we have limited experience of long term ageing but plastic is now the standard way of doing things. Engineering Plastic is a well established and understood material, we are not talking polythene bags here.

.................Dave

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3 minutes ago, mross said:

Its also for recovering wedding rings!  It won't add much cost and could just come in handy one day.

I think a stainless steel tank would be 2 - 3mm, not 6.  6mm tanks are heavy!

I don't think we need the details, but had you eaten it first?

.............Dave

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6 minutes ago, mross said:

No, but I know people who drop things in strange places!  It's a bugger with a dump-through!  A hatch might also be handy if a visitor drops diapers or paper towel in there.

Ours has an inspection hatch near to the suction hose position, I suspect most do. I have not yet needed to open it.....touching lots of wood.

I have been doing a little experiment, and despite what the manufacturers say, it looks like wetwipes etc never dissolve in water.

................Dave

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54 minutes ago, mross said:

Its also for recovering wedding rings!  It won't add much cost and could just come in handy one day.

I think a stainless steel tank would be 2 - 3mm, not 6.  6mm tanks are heavy!

I said 6mm for mild steel because of the corrosion potential. I must sat if a weld in a 6mm mild steel tank leaked after six years then either the welder was useless or all our boats are in imminent danger of sinking. Stainlesswcould be much thinner.

  • Greenie 1
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1 hour ago, Tony Brooks said:

I said 6mm for mild steel because of the corrosion potential. I must sat if a weld in a 6mm mild steel tank leaked after six years then either the welder was useless or all our boats are in imminent danger of sinking. Stainlesswcould be much thinner.

No disrespect, sir, but even 6mm, in steel, is a bit OTT for poo.  I wonder if there is a lifelong, poo-proof coating?  In theory, the tank should be designed merely to withstand the stresses due to the weight of the contents and the likely accelerations.  A well-coated steel tank of 1 mm, or less, would suffice.  

Edited by mross
punctuation
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At Crick boat show someone on the Leesan stand told me they had stopped using stainless steel holding tanks as they had a problem with internal corrosion, they first noticed when an odd coating of something formed on the outside, turned out to be toilet paper seeping through tiny perforations in the metal. 

Polypropylene is impermeable and doesn't corrode. 

Edited by nb Innisfree
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12 minutes ago, nb Innisfree said:

turned out to be toilet paper seeping through tiny perforations in the metal.

Must have been quite big holes!  Sounds improbable to me.  I can imagine something that looked liked Papier-mâché on the outside, but it was probably just poo.

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3 hours ago, mross said:

Its also for recovering wedding rings!  It won't add much cost and could just come in handy one day.

I think a stainless steel tank would be 2 - 3mm, not 6.  6mm tanks are heavy!

Lee Sanitation use to sell a tank inspection hatch as I fitted one in my tank. I can't say I have ever noticed a wiff come from it but I have never tried to open it ether.

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2 hours ago, mross said:

No disrespect, sir, but even 6mm, in steel, is a bit OTT for poo.  I wonder if there is a lifelong, poo-proof coating?  In theory, the tank should be designed merely to withstand the stresses due to the weight of the contents and the likely accelerations.  A well-coated steel tank of 1 mm, or less, would suffice.  

I agree but in my experience coating always eventually fail so if I wanted a mild steel tank I would want it to last a very long time. After all why do we not make our hulls out of well coated 1mm steel. Even the Dutch seem to use 3mm as a minimum on some of their cruisers. Although the poo tank shoudl normally be in the dark I have some concerns over how plastic will age as well.

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The tank may experience some negative pressure if the user has overfilled it and got the vent pipe full before he noticed. Then when pumping out there is no airway for a while until all the goo is sucked back down the vent pipe which will be smaller than the big suck pipe you have plugged into. 

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Both of the two shared boats we had, had 6mm mild steel tanks. 

No issues in 11 and 12 years boating with them respectively. At least 2 current owners of the second shareboat are on this forum, so perhaps they could tell us if the tank has perforated yet. I suspect not.

Of more concern to me would be having a waste tank that utilised the bottom and side of the hull for two of its sides. Failure then ensures costly hull repairs as well as a leaky tank. 

My current boat has a 3mm thick stainless steel waste tank and a 3mm thick stainless steel. Both tanks now 10 years old with no issues so far. 

Edited by cuthound
To unmangle the effects of autocorrect.
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