I installed a new water tank and had to use some of the old iron plumbing pipes which I could not disconnet (30 years of rusted joints). Now the joint between the old pipe and the new check valve has a minor leak, couple drops a minute.

Is there any way to stop the leak without taking the whole connecting job over? Is there anything that I could buy to seal the pipe joint? I heard some time ago advertising on TV about some miracle putty that hardens and could be used to stop water leaks. Has anybody used it and knows where to get it?

I would appreciate any help.