Unless the porcelain is polished, it likely won't benefit from being sealed. The grout is what you need to concern yourself with. Use a brush or applicator to apply the sealer to the grout, let it soak in per the directions (usually around 5 minutes), then polish it dry with a clean white rag BEFORE IT DRIES ON THE SURFACE. A high quality sealer like StoneTech's "Heavy Duty Stone Sealer"
(click here for sealer) is a good choice for grout.
Clean the tile with a nuetral-based cleaner to avoid stripping it from the grout. Find it in the same link to StoneTech products.
As far as mounting the towel racks, you generally use a plastic anchor in conjunction with a screw. Did the towel rack come with a set of screws and anchors? If so, you need to drill an appropriate-sized hole for that anchor. And in very tough porcelain, a diamond hole-saw is a pretty easy solution to just that. Take a look in the
TYW Store again. Click on a picture link to "Porcelain Drill Bits",
then click on "Tile Equipment",
then under the "Tile Drill Bits" is a final link to "Porcelain Drill Bits".
While they seem pricey, they make short work out of a tough job.
