RustOleum's Bulls Eye 1-2-3Â® PLUS Advanced Technology Primer (
) will work very well in bathrooms. It's low odor, water-based and yet seals porous surfaces and protects from water and other stains. Since it's bathroom, you may want to look at their JOMAXÂ® mold and mildew stain remover
to prepare the surface and also use mold and mildew resistant paint, such as Zinsser Perma-White :
Pretty much every big box (and those good small ones, too) hardware store carries these products. I'm attaching the product pictures below to simplify your shopping.