Polyethylene tank repair

richard5933 · April 30, 2018, 04:44:38 PM

So our 4108 has two holding tanks, one for fresh water and one for waste. Both at 43"L x 19.75"W x 25.75"H and hold about 90 gallons. They are made from 3/8" polyethylene with two internal baffles. They were 'welded' together and there are two visible welding beads on the outside of all joints. Not sure about what's on the inside of the seams.

Other than having screw-on flanges instead of spin-weld, they are not that much different than those made today.

The overnight temps finally got warm enough to fill and test the tanks. All is good, until I notice a pin-hole leak at one of the upper corner seams. Nothing serious, but when I filled the tank to the overflow there was a trickle. I pulled out my soldering iron, installed a brand-new wide/flat tip, and proceeded to melt the welding beads into the pin hole until it was filled. That seemed to fix that leak.

Today I refilled the tank to see how things were doing. The corner still held. Then I noticed that in addition to the pin-hole at the corner there was about a 6-inch stretch along one of the top side seams that was apparently never really bonded and that had separated. The side panel sticks up about 1/4" past the horizontal top panel, and the welding seam where they joined just didn't seem to have held. From the discoloration in the gap, I'd guess that the seam had been separated for quite some time.

So, I again took out the soldering iron and proceeded to melt the 1/4" sticking up above the seam with the bead left by the original weld. When I was done, the side seemed firmly bonded to the top panel.

I've got a pack of 1/8" poly welding rods on order. When they arrive I plan to heat an old butter knife with a torch and 'weld' the rod into the questionable seam to build it up a bit in the space still left where the side is sticking up above the top.

Anyone have any suggestions or corrections to what I'm doing? I've never worked with poly before but it seems pretty amenable to bonding by heat. I want to make the tanks last till the end of the season since the budget is pretty well spent right now.

I found a place in PA that makes custom tanks (Miller Plastics), and they will charge about $730 for each of the two tanks. If anyone has suggestions for a better source for custom tanks I'm all ears.

chessie4905 · April 30, 2018, 07:43:44 PM

Harbor Freight sells a plastic welding kit. My brother made his tanks out of platic and welded them together years ago. Never had any leaks. He didn't use the HF though. They weren't around except in Ca. then.
If you Google plastic welding, there is plenty of info about it and what rod to use with the plastic you have and how to identify it.

Iceni John · April 30, 2018, 08:41:28 PM

$730 for a 90 gallon tank seems really high to me. I had Ronco Plastics in Tustin CA rotomold four tanks for me a few years ago, and they charged me $2.50 per gallon (400 gallons of tanks for $1000), so a good local rotomolder should be able to make a 90 gallon tank for maybe $250 to $300, including spin-welding on however many fittings you need. Are you sure that Miller Plastics in PA actually makes tanks themselves, or do they simply resell tanks that are made elsewhere? Something else to watch for are A) do they use virgin polyethylene?, and B) how thick are they? (you want at least 5/16", ideally 3/8"), and C) will they spin-weld on as many fittings as you want exactly where you want them?

John

eagle19952 · April 30, 2018, 10:59:03 PM

ronco

http://www.plastic-mart.com/category/4714/ronco-rv-holding-tanks

richard5933 · May 01, 2018, 04:05:12 AM

The tanks we have now are fabricated from flat sheets, not roto molded. That's what Miller was quoting to replace. I got one other quote from a company in Florida (also for a fabricated poly tank) and their quote was slightly higher at $780/ea.

So far the sites I've seen with roto molded tanks listed as 'custom' were just giving a list of their standard sizes to choose from, none of which would maximize the capacity of the space we have available and still fit to the plumbing already installed. What they mean by 'custom' is just adding the fittings to the locations I need them, not making the take itself to the size I need.

Any of these roto molding places that can actually make a custom size tank?

I did find a plastic welding kit on Amazon last night for about $75 which looks like it's capable of welding the 3/8" material in our tank. Don't think it would do it day after day, but for my needs it should work. I'll stop today at Midland Plastics and pick up some poly sheet cut-offs from their bin to use to practice on. Who know, maybe I'll get good enough at this to just build the new tanks myself.

chessie4905 · May 01, 2018, 05:10:16 AM

I wonder what a metal fabrication shop would charge for ss.

brmax · May 01, 2018, 06:50:50 AM

In my interest with all the builds and many of your multiple coach builds. I found a lot or most of the tank builders and even some of the suppliers/builders are really something good.
What's a hurdle is freight being the tanks sizes we always need in the coach builds. In that I understand truck freight is realy effecient actually, but its always a tough one.
I remember admiring the quality of some that custom built their own tanks with welding these plastics, it clearly was top level.
Their pictures and detail like many of the builds did have some great tips. I recall some used or had to use a freight company. Another member was able to pick up material their self. A couple people had interesting to me, and many Im sure articles discussing some excelent welding tips accrued from the factory people. This was discussed included some welding rods with plastics for these builds. Just really cool for sharing their build, Thanks!

Good day everyone

Floyd

Geoff · May 01, 2018, 07:32:30 AM

I have a plastic welder and always seem to have a tiny leak on poly tanks when welding. I have found that Seal All works the best for fixing non-stress leaks.

ol713 · May 01, 2018, 09:54:32 AM

HI;
Also try ARDEMCO. They are an advertiser in BCM.
800/253-0115.
Merle.

eagle19952 · May 01, 2018, 11:11:36 AM

I went with two 45 gallon tanks... what is normally listed as the height (smallest dimension) , i use as the width. installing tanks flat (horizontal plane) doesn't work for me.

scanzel · May 02, 2018, 03:39:43 AM

I ordered my 110 gallon tanks from Plastic Mart $500 for the tanks and $500 to ship them to Connecticut. Because of the size of my tanks I also enclosed them in a 3/4" box to prevent them from expanding when filled. I don't use tank monitors so I left a small vertical opening to monitor how full they are especially the black/gray.

chessie4905 · May 02, 2018, 04:11:40 AM

mine are enclosed in plywood boxes and have tank monitors about every 4 inches, both tanks.

windtrader · May 02, 2018, 11:38:53 AM

In the event I need a cheap new liquid tank, I'd explore repurposing those 280 gallon caged plastic vessels used by commercial suppliers to ship bulk fluids. For example, my son works in water treatment and the boss wants anyone to just take them away, now stack 80 large. It seems one could fairly easily cut down the container to size then have the two halves joined for strength and waterproofness. It seems some metal strapping 1.5" wide could be wrapped around the outside and with enough proper sealant and screws could make it waterproof. just some random thoughts. Maybe a couple hundred all in.

eagle19952 · May 02, 2018, 02:01:35 PM

enclosed them in a 3/4" box to prevent them from expanding when filled.

i simply centered vertical 2x2's between the tanks and on the exposed surface and secured the tanks with ratchet straps. easy in easy out...they don't expand when filled.

richard5933 · May 02, 2018, 04:43:21 PM

Lots of good suggestions on alternative replacements. Anyone have any advice before I start my on-the-job training with the plastic welding kit? I'm going to try and keep these tanks alive through this season since the budget doesn't have room for a replacement right now.