Help! - gash in black tank

if youcan get to the split take it and get it plastic welded

Personally, I would replace it. Call a mobile repair guy if you need to or take it to an RV repair place.

Having gone trough similar with a fresh water tank I can tell you from my efforts that;
You will be hard pressed to find a plastic welder willing to warranty the work.
The older the tank the less likely that the welding will work.

You could probably find a replacement tank by calling the manufacturer of your rig otherwise EBAY has a lot of RV tanks for sale

There is a You Tube video of a Airstream restorer patching a tank with a propane torch. Look it up and see if you want to try it. If it doesn't work what are you out? I think it's Airstream Planet

Use a piece of 4inch wide x 2 feet roof seam tape Eternabond or Dicor.

They say you can seal an aquarium with the stuff. Cheap to try.

Pogoil.

Black ABS plastic? If so use Plasti-mend for a permanent repair.

White polypropylene? Could weld but that big probably says new tank.

JB Weld

You have got several good responses on how to possibly repair the tank. I'd pick the one that you are most comfortable with and attempt it as none are very expensive. Then fill it up with clean water and see if it holds. If it does great if not then you are out only a minimal amount of money and your time.

By the way I purchased a roll of the Eternabond tape that is 8 inches wide from a local roofing company very cheap. I would try a patching compound like the JB Weld and then cover it with the Eternabond.

Thanks for all the great tips folks. Hey, how is that Eternabond tape?

You never want to have to remove it. I did have what they called a bad batch that came apart easily. The new stuff they sent is there forever.

Pogoil.