Want to modify a fresh water tank.

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Want to modify a fresh water tank.

Postby daveesl77 » Wed May 24, 2017 7:28 am

To begin, our "onboard" fresh water system consists of two, 5 gallon plastic cube type water jugs from wallyworld. I modified the lids and they work ok, giving us 10 gallons feeding into a pressure pump.

With that said, when I did my RV junk yard scavenge almost two years ago, I found a 38 gallon, standard RV, fresh water tank and got it for $10. It has been sitting on a shelf, fully cleaned and sealed, since I got it. And that drives me crazy. Here is a perfectly good, but admittedly very large water tank and it does nothing but sit on a shelf. So my thought is to modify it, to cut it down to say, 10 gallons or maybe a bit more. Its circumference measurement fits perfectly in the space where I presently keep the two water jugs, it is just really long.

So, the idea is to cut it down, then to seal the end up to make it a smaller tank. Does anyone know the proper way to "weld" one of those white plastic (I assume poly) water tanks? Or am I asking for trouble?

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Re: Want to modify a fresh water tank.

Postby Nobody » Wed May 24, 2017 9:37 am

Dunno exactly what you have but, in my experience most fresh water tanks that are not metal, are made of some kind of polyethylene or polypropylene. Neither accepts adhesive very well. Most poly items are bonded with heat using special, item specific bonding methods/equipment. If you aren't set-up to bond the particular tank you have, I think I'd either use it as is or try to sell it to someone that might be able to use it. I don't personally know of any adhesive that works effectively with poly material... We've used a 7gal square, Aqua-tainer from WalMart successfully for over 10yrs. Just refill it when necessary.

If you can acquire a commercial grade 'plastic' welder, you MIGHT be able to achieve a suitable joint. I'm not sure I'd trust it with water tho. That's a lot of weight (10 Gal + approx 82lbs) especially sloshing around when only partially full. I think you may just be asking for trouble but than again, I've never been particularly adventurous when it comes to things I'm not really qualified for.

Good luck on whatever you decide.
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Re: Want to modify a fresh water tank.

Postby Shadow Catcher » Wed May 24, 2017 6:16 pm

I have not done it my self but a proper plastic weld is as strong as the original tank. The question is will you save any money.
The Harbor Freight welder is $50, with some risk in can you get it right , I do not know if I would trust my own work and I know how to weld. You can look for a plastic welder in your area, there are a couple in the Toledo area.
The other alternative buy a new one, search RV water tanks some in the $50 and you can specify inlets etc. Try Ebay one 10 gal at 33.79 with shipping.
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Re: Want to modify a fresh water tank.

Postby lrrowe » Wed May 24, 2017 8:43 pm

I had a serious lapse in good sense awhile back and screwed a screw through a wall right into my plastic water tank. And I did not catch this problem (leak) until my a recent outing to First Landing, VA. I plugged it using a heat source (propane touch). I to gently melted the plastic around the hole with the touch. The plastic would melt, but not fill in the hole. I ended up using of all things, an archery arrow flecthing melt stick and plugged the hole. It seemed to hold up well enough through the tests I ran. I also using a larger piece of plastic sheet to cover the whole side and used silicone sealant as a cement.

I use this explanation as a small encouragement that you can fuse the plastic together.
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Re: Want to modify a fresh water tank.

Postby MtnDon » Thu May 25, 2017 12:05 am

Build a bigger trailer for it. :lol:
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Re: Want to modify a fresh water tank.

Postby daveesl77 » Thu May 25, 2017 6:57 am

MtnDon, perfect answer! ha ha.

I wasn't sure if anyone knew some trick to doing something like this or not. The original idea was that I would carry it in my truck bed and if going somewhere that would have very limited access to water I could fill the entire tank and be able to go for many, many days. Truck is gone now, and while it would easily fit in the van, the physical size is just too big for what I want.

Wife to me when I brought it home - "Why did you buy that thing?"

Me to wife - "But it only cost $10 and look how much water it can hold"

W2M - "Where are you going to put it?"

M2W - "I don't know, but it only cost $10"

:D

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Re: Want to modify a fresh water tank.

Postby lrrowe » Thu May 25, 2017 7:05 am

If you were closer to me, I would offer to buy it from you. That size would fit my plan to carry extra water in my truck and pump it to my CT tank when going off the grid.
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Re: Want to modify a fresh water tank.

Postby Andrew Herrick » Wed Dec 19, 2018 11:43 am

Old thread, but new info: RV tanks come in two flavors: polyethylene (white) and ABS (black). Fittings for polyethylene tanks have to be spun-welded (not something easily done at home) or molded into the tank. Fittings for ABS tank can be glued (fused) with the appropriate adhesive.

IMHO, re-welding a polyethylene or ABS water tank is asking for trouble :D A new tank is probably rated for 80-100 psi minimum + a big safety factor. Would be dastardly difficult, if not impossible, to get that high on a home re-weld.

Only takes one leak to cost more than a new tank, lol! You can buy freshwater tanks for less than a $100 online, some for as low as $50.
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Re: Want to modify a fresh water tank.

Postby daveesl77 » Thu Dec 20, 2018 8:08 am

While I no longer have the tank, it did come in handy a couple of times during hurricanes. In storm prep I filled it, along with my other water tanks, with potable water in case we lost municipal water. Never lost water, but it was nice to know I had that much sitting and easily accessible. So for the $10 I spent, it was worthwhile.

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Re: Want to modify a fresh water tank.

Postby Tomterrific » Thu Dec 20, 2018 11:06 am

Welding plastic. The project is no longer but a strip of the plastic tank would be cut so the exact plastic could be used in the weld. Body shops use plastic welders to repair bumper covers and other plastic bits. This may be the place to find an expert plastic weldor with good equipment.

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