The last thing that you want to do with a tub with an enamel finish is to use anything too harsh. If you do, you could end up taking some of the finish off, which could cause staining or even lead to a leak over time. To clean this type of tub, you simply need to pick your favorite bathroom cleaner and mix it into a bucket of warm water. From there, simply take a sponge or washcloth and scrub out the tub. If there are stuck on stains, you can use a scrubber of some kind, but be as gentle as possible so as to not hurt the coating.