Fresh water tank: ABS or Polyethylene? - Fiberglass RV
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Old 05-15-2021, 03:21 PM   #1
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Trailer: 1971 Compact Jr
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Fresh water tank: ABS or Polyethylene?

Sadly, the original 10 gal. ABS fresh water tank on my '71 Compact Jr. has a crack/leak. I'm guessing this means the tank needs to be replaced, so I did some online hunting, and found an ABS tank with the same footprint (8"x16"x24"), but would need holes drilled and fittings glued on. I also found a "rotational molded polyethylene" tank that isn't quite the same footprint (10"x14"x17") but will fit where the old one was, and it comes with fittings so no cutting/gluing.


The big question for me is, which material is better for fresh water tanks? What I'm looking for is durability and ease of installation so that I don't have to do this again in my lifetime
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Old 05-16-2021, 10:59 AM   #2
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Originally Posted by Dail View Post
Sadly, the original 10 gal. ABS fresh water tank on my '71 Compact Jr. has a crack/leak. I'm guessing this means the tank needs to be replaced, so I did some online hunting, and found an ABS tank with the same footprint (8"x16"x24"), but would need holes drilled and fittings glued on. I also found a "rotational molded polyethylene" tank that isn't quite the same footprint (10"x14"x17") but will fit where the old one was, and it comes with fittings so no cutting/gluing.


The big question for me is, which material is better for fresh water tanks? What I'm looking for is durability and ease of installation so that I don't have to do this again in my lifetime
There is a company in California called Ronco Plastics. They will make a water tank for you to your specifications. I'm sure they will recommend the correct material to you.
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Old 05-16-2021, 12:57 PM   #3
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Neither abs nor polyethylene are lifetime tank materials. Both may crack. The tank is much less vulnerable if installed inside the trailer. Also better if the tank is well supported and the connecting pipes are well supported.

I would choose the ABS tank. Polyethylene is more difficult to repair because very few adhesives stick to it. Polyethylene welding may or may not hold. I am attempting to repair the polyethylene grey tank installed under my trailer. It has multiple cracks caused by impacts. Tried welding but it didn't hold. Now planning to try either West System G/flex 655 adhesive or J-B Weld 50133 Plastic Bonder adhesive.

You could try repairing your tank with an ABS adhesive.
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Old 05-16-2021, 01:18 PM   #4
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Simply ask the ABS manufacturer if that tank is approved for potable water. If not, there's your answer. They might even install fittings for you. ABS can be glued, and is glued together in piping system, such as the black water piping in most trailers.

Polyethylene is approved for drinking water.

Tank fittings in Poly tanks are "spin welded". That method is way different than a typical "weld", and will not fail unless the later pipe fittings are incorrectly installed and crack the spin welded fitting.

If your new tank has an access hole, you can reach in and install bulkhead fittings that do not need glue, but instead have a gasket and a nut.

One of the reasons Poly is so good, is that it is inert. It cannot be glued by any glues I'm aware of, and certainly not the common epoxies. It will also become brittle and crack if exposed to UV or high doses of chlorine.
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Old 05-16-2021, 06:12 PM   #5
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The 2 ABS tanks previous owner installed under my Casita, mounted with screws through flange into plywood floor both cracked at flange.
Almost lost one on return trip from west coast but held together long enough to make it home.
Replaced with Poly tank that I had made a rack out of angle iron and hung this rack from frame with 3/8 rod from pipe hangers.
tank now sits on it's own rack suspended between frame.
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Old 05-17-2021, 09:14 AM   #6
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Colorado
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Originally Posted by Dail View Post
Sadly, the original 10 gal. ABS fresh water tank on my '71 Compact Jr. has a crack/leak. I'm guessing this means the tank needs to be replaced, so I did some online hunting, and found an ABS tank with the same footprint (8"x16"x24"), but would need holes drilled and fittings glued on. I also found a "rotational molded polyethylene" tank that isn't quite the same footprint (10"x14"x17") but will fit where the old one was, and it comes with fittings so no cutting/gluing.


The big question for me is, which material is better for fresh water tanks? What I'm looking for is durability and ease of installation so that I don't have to do this again in my lifetime
The first major consideration is it good for potable water. Not all tanks are good for drinking water. All tanks would hold water but not be safe to drink or use for anything going into your mouth.
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Old 05-17-2021, 02:32 PM   #7
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For those following along at home I ended up choosing the ABS tank, and the reason was simple. To check on locations for hoses/fittings/ets, I made a cardboard mockup of the Poly tank I was considering, and that was the best idea I had -- doing that I discovered that to use the Poly tank (all of which are at least 10" high), I'd have to relocate the fill fitting on the side of the trailer, and that was something I really didn't want to do, so to avoid a cascade of changes I didn't want to make, I went with the ABS tank which is 8" tall and will fit where the original was with no change to fittings or fasteners to keep it in place.
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Old 05-23-2021, 09:47 PM   #8
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Originally Posted by John in Michigan View Post
Neither abs nor polyethylene are lifetime tank materials. Both may crack. The tank is much less vulnerable if installed inside the trailer. Also better if the tank is well supported and the connecting pipes are well supported.

I would choose the ABS tank. Polyethylene is more difficult to repair because very few adhesives stick to it. Polyethylene welding may or may not hold. I am attempting to repair the polyethylene grey tank installed under my trailer. It has multiple cracks caused by impacts. Tried welding but it didn't hold. Now planning to try either West System G/flex 655 adhesive or J-B Weld 50133 Plastic Bonder adhesive.

You could try repairing your tank with an ABS adhesive.
Hubby says you can weld polyethylene he is has done many over the years. Did many an RV's traveling the Alaska highway when water and septic tanks cracked or with holes in them. He says NO adhesive will hold polyethylene period. ABS is easy to weld, but very brittle, polyethylene is very strong. All that said we had an stainless steel one made for our boler.
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