You will need to sand it down and clean it real good. You can either paint it with a vinyl paint or have it sprayed with spray on bed liner or pond liner. Wal-Mart here has a roll-on bed liner. It's $100.00/gallon. I plan to use it on my 6'diameter galvanised stock tank.

Happy ponding,
Scott

cfsam, did you put fish in it after that?

I do remember those evaporative coolers, but bet that tar is hard to find here where it is so humid.

marti8a, I let the tar set for 3 days then I filled the stock tank. Then I treated the water for chlorine.

Since I wasn't sure if it was safe, I bought some feeder goldfish and put them in there.

They did fine so after a couple of weeks, I put some of my regular fish in there and added the waterlilies.

You are right. That tar might be hard to find in humid areas.

My DH takes a wire brush and cleans the rust out of the tanks. He solders any pin holes then he washes the tank off and lets it dry well. If he thinks it needs it he runs a thick bead of clear silicone around the bottom inside seam and lets it dry for at least 2 or 3 days. DH buys spray cans of automotive undercoating at the parts store. He sprays the outside bottom of the tank and sometimes if the tank is really bad, we spray the inside bottom with it as well. If the tank isn't too bad I've used Krylon spray primer on the inside of the tanks to help protect from rust.
I've kept water lilies and goldfish in old tanks done this way and had no problems. So far, a couple of my tanks are going on their 3rd year and still holding.

marti8a, one of my large stock tanks is about 20 years old and is still okay, except for some tar patches. The other large one is about 14 years old. Then I have a newer one that is only about 4 years old.

Out on ranches, these stock tanks last for 50 years or more. Of course they are sitting on the ground instead of being buried which is probably better for the tank.

It sounds like your DH and you have a good system going for repair work.

I wanted another stock tank to put lilies in with no pump or filtration. Hubby had one at the farm that was beyond repair. The bottom was loose about 1/4 way around and it had some holes in the bottom about as big as a pop can. I lined it with old carpet and used a $15 kiddie pool for a liner. So far it is doing great. I'm not even loosing any water to evaporation. I didn't want to use a kiddie pool alone because there are dogs that run free in our neighborhood and I was afraid they would destroy it. The liner fit my 8' tank perfectly, but just not all the way to the top.

cfSam, if you are talking about our system of me making suggestions & dh doing the work, you're right! lol

marti8a,that is the way it works around my house too. My wife supervises and I do most of the work. LOL

I think it turned out ok. Dh used an epoxy for metals. The only complaint I have is that it is white, but I'm sure that will be green soon enough. Haven't put any fish in it yet; that will be the test.

You could have gone to a paint store and got some pigment.

Happy ponding,
Scott