Poly Water Tank Repair

You might be able to weld it...

https://www.youtube.com/results?search_query=welding+black+polyethylene

...or you might consider gluing a patch on the inside...

https://www.interstateplastics.com/Hdpe-Black-Sheet-HDPBE~~SH.php?thickness=0.125&dim2=12&dim3=12&src=adwordspla&utm_source=froogle&utm_campaign=froogle&utm_medium=na&utm_content=plastic%20sheets-HDPBE%20SH&gclid=CjwKCAiAu9vwBRAEEiwAzvjq--ze_29GxSaKhUtbFtq8J0FFBTD2Hyz12iAyce5FRwPDPBe9BfbpPxoCvM0QAvD_BwE

https://www.homedepot.com/p/Loctite-Plastics-Bonding-System-2g-Super-Glue-681925/100371829

....or you might do both...

https://www.extension.purdue.edu/extmedia/PPP/PPP-77.pdf

These folks might be able to help you.

http://arrowpumpcompany.com/water-tanks/3310727

Arrow Pump Company L.L.C.

3803 West Orangewood Drive

Tucson, AZ 85741

Good luck with your quest.

There are a number of apparently great new tapes advertised however I have not used them on your application but from your description the force of the head of water is part of the problem, Is it possible to place a metal band around the tank to help with the water force. One company that has good products is the Gorilla line of products. I would lower the water and place multiple layers on the inside.

Also when I was in the business of stopping water leaks in concrete there were quite a few manufacturers of water activated foams even better when used with an activator. these can be brushed on and I used multiple layers of cloth both polyester and fiberglass to act as a membrane. I think you can do this repair quite reasonably but the metal band probably will allow the repair to last much better. Just as many silos use metal bands or hoops to reinforce to prevent inside forces from bursting the structure.

One possible method is to provide a clamp round the tank that could tightened and place a flexible packing wad right where the leak is .

This would prevent not only the leak, but also distortion due to water head .

Assuming you can empty the tank to below the leak, almost any patch on the inside will be held in place by the water pressure: a bycicle innertube repair kit would probably work, because your not trying to "span" a gap (the original structure holds a head of over three feet).

I suspect that the side has been damaged by a heavy blow. If you think that the area of the leak needs strengthening, then, after stopping the leak as above, epoxy a large plate over the area, and, hold that in place with a band round the whole tank. You might need to put a "lump" under the band inthe middle of the plate to ensure a good inward force.

On steel tanks, I used to use fiberglass cloth and its resin. More recently I have had good luck with "Flextape." The water level should be lowered below the leak so the surface is dry and clean. Cut the appropriate size of tape, then stick it on the outside. I used a linoleum roller to assure it was well adhered. A second patch on the inside would be good insurance, but remember dry and clean.

Flextape should stick to the plastic with no problem, but some glues will not. Flextape has a plastic sheet protecting the stickum; it can be difficult to get an edge or corner started but then is easy to get off.

The only thing that I would add to the smart suggestions already made is that if the water in this tank is used for drinking, make sure the repair you use is likewise compatible. I am not sure if some of the tapes and glues discussed would be.

Good luck.

I'd go with #8.

Seam or pinhole, welding will fix it.

With ''Flexseal'' and/or ''Flextape''?...

https://www.flexsealproducts.com/

I think I did try the Flexseal spray but used a bit of fiberglass cloth as a reinforcement with a spray coat before the fiberglass and another after--after some drying time.

But I thought the Flextape did a better job, and it was less messy to put on.