converting a never used PVC holding tank to water tank, possible?

[CaptainRivet]

Hi all,


i have a new 60l holding tank (the black PVC ones with revision opening) in my boat that was installed 3 years ago by the former owner due to registration/certification requirements.
Tank was defintily never used (former owner confirmed this too), can check the tank through the revision opening. Also all pipes to and from tank are like new. Clear why never used/only for certification as the switching valve was installed under the V-berth and you have to empty the storage to get to the valve to switch it.


I use the boat for a 10year world circum and don't need a holding tank. Tank is in perfect location next to the watermaker under the bench with 60l, higher then the main water tank and 3 m away from it. So I wanna use the "new holding tank" as additional water tank that gets filled by the watermaker, after check the quality i open the valve to transfer it to the main 500l water tank. As tank is higher then main tank no pump needed.

Plan would be:
1) disconnect the pipe that connects toilet out pipe and delete the T-piece/valve, so toilet can not be routed to holding tank anymore and block of the connection on the holding tank.

2) fill yachticon "watertank super cleaner" into "holding tank" (overdose put 100g which is for 100l water) and fill up the whole holding tank + piping with water via the pump out deck opening to disinfect and clean anything that is there. leave it for 2 days doing its magic and flush everthing. repeat once more. use the yachticon product since years for cleaning water tank and all pipes once a year, works really well especially cleaning all the pipes and fittings.

3) change&replace the pump out pipe to the deck fitting from bottom (suck out) to the top of the tank. Aim is it can also be filled directly like the main tank. Also connect the water maker to this pipe/inlet with a T-Valve.

4) lower 2 tank connections:

- disconnect the pipe going to the through hull that flush out the tank. block of the through hull. next haul out deinstall & close the through hull.
- route a new pipe with a block of valve from the holding tank to the main water tank
- block off the 2nd lower connection (was connected to pump out deck fitting)
- venting: block off the venting opening.


OK ?
or is there anything that would prevent me from using the basically new holding tank as additional water tank?


Thanks

[Madehn]

as long as the PVC is foodsafe then i guess it would be ok but most of the time with a watermaker you test product coming out by running it into a sink/bucket etc until you get acceptable product ( usually takes a few minutes) then flip the valve and fill the main water tank directly- simple and easy- now if you wanted to have more water capacity then it might be worth doing.

[CaptainRivet]

Thanks for the answer.
The holding aka 2nd watertank serves 3 purposes.
1) pre tank for the powersurvivor 40E watermaker. The 60l is what it makes max in a day of 10hours running. I test the water in the beginning and at the end of the "daily session". As you described first, if ok water goes in the pre tank. After 10h I test it again, if ok the daily production is transferred to 500l main tank. In 10h a lot can happen and like this i don't conterminate the 500l if sommething goes wrong.
2) support balance of the boat. the 500l diesel tank of the 39ft ketch is from midship back, the 60l holding tank far front in the bow. If diesel tank is full, boat hangs a bit in the back, from half full till empty its even. If i fill the 60l tank full the "hang" with full diesel tank is significantly/mostly reduced.
3) security plus additional 60l water so i have 560l and in 2 tanks, if one is contaminated i still have the 2nd to use. Normally 2 on board so 60l last long.

[LittleWing77]

Originally Posted by Madehn

as long as the PVC is foodsafe..

I would venture to say that a black PVC holding tank would NOT be food safe. Plus black plastic anything in the tropics mean the water would taste like plastic - which would mean you'd be subtly ingesting toxic plastic byproducts in the water.

Do not stint on the safety of your drinking water system!

Get Peggie Hall's book and read up on this. (Search: peghall) She's a Forum Member.
LittleWing77

[peghall]

I've occasionally run across a boat owner who used 6-8" pvc pipe as a holding tank (which almost always turned out to be a bad idea where winters get cold 'cuz PVC, even sch 80 or ABS, gets very brittle when in cold conditions), but I've never seen or even heard of PVC being used to make anything but round pipe and plumbing fittings. Are you sure the tank isn't actually polypropylene? PP is an opaque plastic that's often used to make water or waste tanks because it's easier to cut and, unlike PE which can only be heat welded, can be "glued."

If it is PP, and has never been used, there shouldn't be any reason why it can't be used to hold fresh water.

--Peggie

[endlesspursuit]

So what are you going to use as a holding tank when in a harbor that requires it?

[Ifitsworthdoing]

Can you convert the heads/toilet that’s losing it’s holding tank to a composting one?

[CaptainRivet]

Originally Posted by endlesspursuit

So what are you going to use as a holding tank when in a harbor that requires it?

well was never the case except of the med. on the barefoot route around the world (except of med) there are no pump out stations anyhow. And I officially have it in the reg papers, so no port official will ask/check.
And if thats the very seldom case that a grey water tank must be used, I just use the habour facilities and not the boat one.
And I leave all grey water pipes in, just disconnect and run new pipes to main tank and watermaker. So if I really need to its quickly connected back on as grey water tank.

[CaptainRivet]

Originally Posted by peghall

I've occasionally run across a boat owner who used 6-8" pvc pipe as a holding tank (which almost always turned out to be a bad idea where winters get cold 'cuz PVC, even sch 80 or ABS, gets very brittle when in cold conditions), but I've never seen or even heard of PVC being used to make anything but round pipe and plumbing fittings. Are you sure the tank isn't actually polypropylene? PP is an opaque plastic that's often used to make water or waste tanks because it's easier to cut and, unlike PE which can only be heat welded, can be "glued."

If it is PP, and has never been used, there shouldn't be any reason why it can't be used to hold fresh water.

--Peggie

Thank you Peggie. You are right, its PP. Perfect, so I can use it.

[Differentroads]

You seem sorted out for your decision. A little additional suggestion. Arrange your plumbing so you can isolate and use the contents of this tank for washing only if it turns out to be unpaletable for drinking.

I've got a mix of steel, food grade PP and flexitanks. The water from the flexitanks has a plasticky taste even when I run it through the filter. The water from the solid tanks is fine. So I plumbed a couple of manifolds and valves along with two pumps to enable me to split the flexitank water for washing (oneself and dinner plates etc) and the solid tanks for drinking and cooking water. It works well for us as liveaboard cruisers. Our flexitanks are also plumbed via valves to the deck drains to take rainwater, which I prefer to use for washing rather than drinking. Every tank is able to be isolated via the manifolds and valves for maintenance and to prevent leaks draining all of the fresh water into the bilge.