I think it is about 1/4 cup of bleach per gallon of water.

Remember that reptile enclosures are not designed to hold alot of water like aquariums are. The easiest thing to do is put a couple of inches of bleach and water, scrub it with a rag or sponge, dump it out, then rinse it until you can't smell the bleach anymore. I think the easiest way to rinse is with a water hose. You shouldn't get the UTH wet by doing this. I know it may be too late now, but it is easier to use Aluminum tape to hold the UTH on. It comes off alot easier than trying to un-stick a UTH...