How do you clean grout sealer off bathtub?

finger nail polish remover or acetone should remove the sealant, but there is a chance they would damage the finish of the tub, depending on the material. If it is porcelain it should be fine, but if it is plastic don't use them. WD-40 will also probably work and is probably safer, so you could even try it first. Spray the sealant with WD-40, then let it sit until it is almost dry - probably only 15 seconds or so, then spray again. Rub with a fingernail or plastic scraper. You can use WD-40 on pretty much any surface, and can buy it at Walmart or Target. If the WD-40 leaves a residue, clean it with glass cleaner - may take a couple sessions.