Holding tank problem, is this possible?

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mriley

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For some reason beyond me, the outlet on my holding tank is positioned on the side near the top. This means that whenever I use the hand pump installed for the purpose I can only pump out 1/4 of the contents, if that. This is very frustrating. The tank is galvanised steel, and the outlet is a short stub of 1.5 in o/d pipe welded on (to which the sanitary hjose is clamped).

Ideally, the outlet pipe would be positioned on top of the tank, and extend downwards to near the bottom, but there isn't the headroom to do this. Also, it seems the boat was built around the tank, and it would be impossible to remove or replace it without major structural work including cutting away fibreglass decks.

This is the question: would it be possible to install another outlet pipe fitting on the side of the tank, and if so how. Ideally the pipe would be fitted on the side near the top, and angled downwards at 45 degs extending to near the bottom. Or installed horizontally on the side near the bottom. The tank can be emptied through the hole cut for the level sender fitting, but obviously could not be accessed from the inside. Welding would not seem to be possible because of lack of space/proximity of fibreglass etc. Are there any clever gizmos available?

Any suggestions gratefully received.
 
I have to say, once I was set on improving that area, I'd start by getting rid of the tank. Galvanised steel is not a very good material for holding mixed sewage and seawater, which is one of the more corrosive substances found on a boat. If the pipework is also sub-standard, best to ditch it and re-do properly. Hopefully, if your galvanised tank is rectangular, you'll be able to buy an off-the-shelf replacement in moulded polyethylene. If it's an odd size or shape then Tek Tanks will fabricate a custom one from polyethylene sheet, albeit at a price.

That said, there are plumbing fittings which clamp onto the wall of a tank, so you might be able to bodge something up. See this page for example: http://www.bes.co.uk/products/107a.asp

Pete
 
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Would the tank empty by gravity if it had an outlet in the bottom? This is by far the simplest arrangement for a holding tank. It is perfectly possible to fit a skin fitting in the bottom of the tank, in fact mine has a plastic one that is coping perfectly well. You would then only need to cut a hole of suitable size with a tank cutter hole saw.

I agree with the others that a galvanised tank is far from ideal but I understand your dilemma. Maybe worth investigating an epoxy coating?
 
I agree with the others that a galvanised tank is far from ideal but I understand your dilemma. Maybe worth investigating an epoxy coating?[/QUOTE]

The tank could be aluminium, I just assumed it was galvanised steel - I guess aluminium is a better material than steel?
 
mriley said:
The tank could be aluminium, I just assumed it was galvanised steel - I guess aluminium is a better material than steel?
Click to expand...

Not really. Stainless would probably be the least bad metal, but even that corrodes eventually as it did on our new boat (14 years old). The tank was already leaking before we bought her, and we immediately removed it - in fact (with the vendor's permission) before the sale was actually complete.

10mm polyethylene sheet with hot-air-welded joints is the proper material.

Pete
 
mriley said:
For some reason beyond me, the outlet on my holding tank is positioned on the side near the top. This means that whenever I use the hand pump installed for the purpose I can only pump out 1/4 of the contents, if that. This is very frustrating. The tank is galvanised steel, and the outlet is a short stub of 1.5 in o/d pipe welded on (to which the sanitary hjose is clamped).

Ideally, the outlet pipe would be positioned on top of the tank, and extend downwards to near the bottom, but there isn't the headroom to do this. Also, it seems the boat was built around the tank, and it would be impossible to remove or replace it without major structural work including cutting away fibreglass decks.

This is the question: would it be possible to install another outlet pipe fitting on the side of the tank, and if so how. Ideally the pipe would be fitted on the side near the top, and angled downwards at 45 degs extending to near the bottom. Or installed horizontally on the side near the bottom. The tank can be emptied through the hole cut for the level sender fitting, but obviously could not be accessed from the inside. Welding would not seem to be possible because of lack of space/proximity of fibreglass etc. Are there any clever gizmos available?

Any suggestions gratefully received.
Click to expand...


I expect that at day 1 the tank was assembled with an internal elbow and dipper pipe to the tank bottom to ensure all was pumped
out. This was normal practice but from the top usually. You have reduced headroom so a side entry. This allows plumbing maintenance with out the contents making unscheduled departures to places where not wanted which can happen with a bottom entry. Seems you might have to chop your tank and remove piece by piece.


Polyethelene holding tanks are available from many suppliers as Google will show including Tek Tanks and Vetus
 
mriley said:
For some reason beyond me, the outlet on my holding tank is positioned on the side near the top. This means that whenever I use the hand pump installed for the purpose I can only pump out 1/4 of the contents, if that. This is very frustrating. The tank is galvanised steel, and the outlet is a short stub of 1.5 in o/d pipe welded on (to which the sanitary hjose is clamped). .........
Click to expand...


It seems fairly incredible that anyone would arrange the outlet pipe from the tank, so that only 1/4 of the contents could be pumped out. Are you sure there's not an internal elbow and pipe, facing down towards the bottom of the tank?
 
NormanS said:
It seems fairly incredible that anyone would arrange the outlet pipe from the tank, so that only 1/4 of the contents could be pumped out. Are you sure there's not an internal elbow and pipe, facing down towards the bottom of the tank?
Click to expand...

I'm sure there was when it was built, but quite possibly it has fallen off or corroded through (a fair sized hole near the elbow would prevent any suction going on) if made of unsuitable materials.

Pete
 
NormanS said:
It seems fairly incredible that anyone would arrange the outlet pipe from the tank, so that only 1/4 of the contents could be pumped out. Are you sure there's not an internal elbow and pipe, facing down towards the bottom of the tank?
Click to expand...

Probably there was, though it's possible the bend and pipe to the bottom have come off - that's what happened with mine (and that was in polypropylene)
 
If you want to put another outlet in go to a plumbers merchant & ask for an Essex Flange
It can be inserted from the outside provided you drill the correct size hole
Trouble may be in getting the diameter that you want
 
charles_reed said:
Probably there was, though it's possible the bend and pipe to the bottom have come off - that's what happened with mine (and that was in polypropylene)
Click to expand...

I think that's right - I've poked a long screwdriver into the outlet hole and there's no evidence now of a downward bending pipe inside the tank.
 
Thanks for suggestions of using Essex flange - I hadn't heard of them. The 1.5in size is available with screw fitting only, which I think means I will be able to attach the right sized pipe to the outside of the flange, but not pass one through that bends to the bottom of the tank unless anyone can advise differently (ie flange will need to be at bottom of side of tank). Next worry is effect of tank contents on copper/brass pipes and fittings???
 
mriley said:
Thanks for suggestions of using Essex flange - I hadn't heard of them. The 1.5in size is available with screw fitting only, which I think means I will be able to attach the right sized pipe to the outside of the flange, but not pass one through that bends to the bottom of the tank unless anyone can advise differently (ie flange will need to be at bottom of side of tank). Next worry is effect of tank contents on copper/brass pipes and fittings???
Click to expand...

I was going to suggest an Essex flange but I suspect you will only find them made of brass.

It would be a mistake to put a brass fitting into a galvanised steel holding tank I am sure.
 
VicS said:
I was going to suggest an Essex flange but I suspect you will only find them made of brass.

It would be a mistake to put a brass fitting into a galvanised steel holding tank I am sure.
Click to expand...

The whole set-up is so riddled with testing errors that I'd start from scratch and replace the whole thing if I was in the OP's shoes. Probably with Tek-tank and a properly designed layout.
It looks as though it's shaping up to be a whole sorry story of woe.
 
charles_reed said:
The whole set-up is so riddled with testing errors that I'd start from scratch and replace the whole thing if I was in the OP's shoes. Probably with Tek-tank and a properly designed layout.
It looks as though it's shaping up to be a whole sorry story of woe.
Click to expand...

As I said in my original post, it is not possible to remove the tank, nor is there space anywhere else to install a second tank, which is why I'm trying to find an alternative solution - I'm sure there is one. At the moment I am able to bypass the holding tank and pump straight from the toilet out to sea, but obviously there will be circumstances when it is best not to do this.
 
If you cannot replace the tank with a new plastic I would cut an rectangular access hatch in the top of the tank. Line it with GRP and check on the inlet/outlet fittings. Make up a access hatch cover from the same material tek tanks use.
 
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