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Sealing Old Metal Pump Out Advice - Empty/Dry v. Filled with Water


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I have scoured the forum the best I can, and found a few answers that have informed me, but think I need to ask a fresh question...

 

I have just removed an old plastic pump-out tank - disgusting work but all OK. However, after shifting this tank I discovered that the boat has an older metal waste tank under the floor; possibly built into the hull but I am not 100% sure.

 

The older tank wasn't sealed, with just a piece of wood over the old 'drop-through' hole. I was surprised to find it nearly full to the top with (orange) water. I thought this was old sewage, but having stirred a stick around it doesn't bring up any sludge so am wondering if a previous owner had flushed it out and just left it full of water, which has since mixed with rust.

 

My question is: I want to pump out this old water, but am unsure whether to A) try to dry it out and leave it empty or B) keep it filled with water which I have read in some places will stop the bottom rusting. My gut goes with option A, but I wondered if it would still rust?

 

Any suggestions on what to do to deal with this old tank (without removing it) and sealing it back up would be much appreciated!

 

(If it helps, the boat is an ex-hire Canaltime / South West Durham build from 2000.) Thanks in advance!

 

 

WhatsApp Image 2022-01-13 at 8.23.39 PM.jpeg

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15 minutes ago, matty40s said:

Water and steel = rust, speshly when its rusty already(orange water).

 Suck it all out, dry it, then de-rust it, treat and apply either a decent bilge paint system, or blacking.

 

Thanks Matty - I agree that would be best, too. Treating and blacking it would be ideal, although I am wondering how far into it I can reach, as it stretches the entire width of the boat. A long handled/radiator brush my be a good start... Thanks for your help :)

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3 minutes ago, ditchcrawler said:

Are you sure its a pumpout tank? under the floor would be very shallow and no sign of where a toilet was sealed to it

Unfortunately so - the boat actually had 2 old pump outs - the main one in the bathroom was the same - under the floor, but in much better condition (empty and sealed). These must have been the originals, as newer toilets/plastic tanks were the operating toilets when I bought it. Plus there are the old capped off vents and pump out pipes.
You're right - it's very shallow, but does stretch the width of the boat.

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25 minutes ago, ditchcrawler said:

Are you sure its a pumpout tank? under the floor would be very shallow and no sign of where a toilet was sealed to it

It was very common for hire companies to use welded to baseplate tanks for pump outs and shower drains(with a bilge pump). This hasn't really changed, Black Prince still do it with their 2 toilet massive tank under the central bed system. 

They don't build the boats to last a lifetime, just a hire boat lifetime.

For those Black Prince owners now worried, I would be too. 

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1 hour ago, Hudds Lad said:

Could it have been kept full of water for ballast purposes? be interesting to see how the trim/handling changes once it’s gone

What would happen when they had a pump out?

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So first you had to remove a disgusting old plastic pump out tank and then you found a nasty rusting integral steel waste tank underneath that's full of gawd knows what...

 

Pump out tanks... Just an all round bad idea.

Edited by blackrose
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Just now, ditchcrawler said:

Before the plastic tank was fitted when the poo was in the steel one under discussion.

Yes, but my badly made point was that it’s been floating about with an extra tank of “fluid” underneath for quite some time, once that weight is removed it’s surely going to change things?

I was just speculating on why it was full. Surely nobody in their right mind would leave a tank of the brown stuff there permanently? Other options i guess could be a leak from somewhere that’s filled it, or it had a fill of water and chemicals to sit for a bit to break down any sludge for one last pump out that they then forgot to do?

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I suppose, empty it and see if it refills on its own, then you have a leak.  If not, then clean as well as you can, maybe take up the floor on the other side, if that were possible. Then treat it as well as you can before reinstating the floor, perhaps a new bit of ply would be nice.  Or, would it be easier to coat it up liberally with Rustol-Owatrol  after cleaning as well as you can?  Then sell the boat.

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Empty it

Dry it out

Treat it with rust preventer of your choice

Carefully fill with Sprayfoam.

 

I have done the first two with mine, but after 7years haven't got round to doing the last two 😱

 

 

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5 hours ago, Alan de Enfield said:

Or, it could just be a bilge full of rusty water slowly eating its way from inside to outside.

 

Good point. How deep it is would seem a useful test - if it's only a couple of inches of space between floor and baseplate it is highly unlikely to be a pumpout tank.

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Doesn't look like a pumpout tank to me, just a bilge full of rusty water. Where is this along the length of the boat?  If this is not at the stern, can you access the bilge  at the stern end of the cabin? Is that wet or dry?

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4 hours ago, Hudds Lad said:

 . Surely nobody in their right mind would leave a tank of the brown stuff there permanently? Other options i guess could be a leak from somewhere that’s filled it, or it had a fill of water and chemicals to sit for a bit to break down any sludge for one last pump out that they then forgot to do?

Now that is a very good question.

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On 14/01/2022 at 20:39, matty40s said:

It was very common for hire companies to use welded to baseplate tanks for pump outs and shower drains(with a bilge pump). This hasn't really changed, Black Prince still do it with their 2 toilet massive tank under the central bed system. 

They don't build the boats to last a lifetime, just a hire boat lifetime.

For those Black Prince owners now worried, I would be too. 

Although this isn't what I wanted to hear, I was expecting this! It makes sense to know this was (still is) the practice. Many thanks

 

On 15/01/2022 at 07:33, Alan de Enfield said:

Or, it could just be a bilge full of rusty water slowly eating its way from inside to outside.

It's definitely an isolated tank, as I can feel and see the edge under my kitchen floor (and there is no water in the bilge there). But yes, what you say about it slowly eating its way from inside to outside is still my main worry...

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On 15/01/2022 at 13:40, David Mack said:

Doesn't look like a pumpout tank to me, just a bilge full of rusty water. Where is this along the length of the boat?  If this is not at the stern, can you access the bilge  at the stern end of the cabin? Is that wet or dry?

This tank is half way down the length of the boat - the tank is full width of the boat. Unfortunately, it does seem to be a tank and not the bilge - I can see and feel the edge through the kitchen floor and there is no other water in the bilge in the rooms next to the tank. Plus there is the metal 'top' with just the square toilet drop through hole to access it.

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