Mitchellmoxo Posted September 25, 2017 Report Share Posted September 25, 2017 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 Link to comment Share on other sites More sharing options...
dmr Posted September 25, 2017 Report Share Posted September 25, 2017 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 Link to comment Share on other sites More sharing options...
Tony Brooks Posted September 25, 2017 Report Share Posted September 25, 2017 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. Link to comment Share on other sites More sharing options...
Mitchellmoxo Posted September 25, 2017 Author Report Share Posted September 25, 2017 Great thanks and what thickness would you go if stainless? Link to comment Share on other sites More sharing options...
mross Posted September 25, 2017 Report Share Posted September 25, 2017 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. Link to comment Share on other sites More sharing options...
dmr Posted September 25, 2017 Report Share Posted September 25, 2017 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. .............Dave Link to comment Share on other sites More sharing options...
dmr Posted September 25, 2017 Report Share Posted September 25, 2017 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 Link to comment Share on other sites More sharing options...
linnit Posted September 25, 2017 Report Share Posted September 25, 2017 1 hour ago, Mitchellmoxo said: Great thanks and what thickness would you go if stainless? I fabricated mine in 3mm 316 grade..however 304 grade would probably be fine Link to comment Share on other sites More sharing options...
dmr Posted September 25, 2017 Report Share Posted September 25, 2017 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 Link to comment Share on other sites More sharing options...
mross Posted September 25, 2017 Report Share Posted September 25, 2017 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. Link to comment Share on other sites More sharing options...
Cheshire cat Posted September 25, 2017 Report Share Posted September 25, 2017 A boat we had a share in had a plastic tank fitted 15 years ago. No problems so far. The seams rotted through on the mild steel predecessor after six years. Link to comment Share on other sites More sharing options...
dmr Posted September 25, 2017 Report Share Posted September 25, 2017 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 Link to comment Share on other sites More sharing options...
mross Posted September 25, 2017 Report Share Posted September 25, 2017 I reckon wet wipes could probably destroy the pump out station's pump. It burnt out earlier this year at our marina. I wonder if it had a rubber impeller? Link to comment Share on other sites More sharing options...
mross Posted September 25, 2017 Report Share Posted September 25, 2017 Why not ring these guys, who will build you a tank to your exact requirements? http://www.hendersons.co.uk/boattank/plastic-wastewater-tanks.html Link to comment Share on other sites More sharing options...
Tony Brooks Posted September 25, 2017 Report Share Posted September 25, 2017 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. 1 Link to comment Share on other sites More sharing options...
mross Posted September 25, 2017 Report Share Posted September 25, 2017 (edited) 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 September 25, 2017 by mross punctuation Link to comment Share on other sites More sharing options...
nb Innisfree Posted September 25, 2017 Report Share Posted September 25, 2017 (edited) 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 September 25, 2017 by nb Innisfree Link to comment Share on other sites More sharing options...
mross Posted September 25, 2017 Report Share Posted September 25, 2017 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. Link to comment Share on other sites More sharing options...
ditchcrawler Posted September 25, 2017 Report Share Posted September 25, 2017 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. Link to comment Share on other sites More sharing options...
Tony Brooks Posted September 25, 2017 Report Share Posted September 25, 2017 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. Link to comment Share on other sites More sharing options...
Detling Posted September 25, 2017 Report Share Posted September 25, 2017 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. Link to comment Share on other sites More sharing options...
cuthound Posted September 25, 2017 Report Share Posted September 25, 2017 (edited) 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 September 25, 2017 by cuthound To unmangle the effects of autocorrect. Link to comment Share on other sites More sharing options...
Sea Dog Posted September 25, 2017 Report Share Posted September 25, 2017 10 hours ago, mross said: Also, fit a good hatch on top for cleaning out. Noooo!! I know it's not like you to give poor advice, but I think what you meant to say is: "fit a good hatch on top in case you need to get someone else to clean it out". Link to comment Share on other sites More sharing options...
mross Posted September 26, 2017 Report Share Posted September 26, 2017 11 hours ago, Sea Dog said: Noooo!! I know it's not like you to give poor advice, but I think what you meant to say is: "fit a good hatch on top in case you need to get someone else to clean it out". Why do you say that? I've been inside sewage tanks before! Link to comment Share on other sites More sharing options...
junior Posted September 26, 2017 Report Share Posted September 26, 2017 If i were you I'd save your money and get a cassette toilet. Much better option. Link to comment Share on other sites More sharing options...
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