Some clarification if you haven't already drilled your holes (and for others considering something similar): if the tiles are actually porcelain and not just ceramic, a regular carbide bit suggested by others may not be hard enough to penetrate. Porcelain tiles are harder than conventional ceramic, and usually require a diamond-tipped drill bit. A bit pricier than carbide-tipped, but well worth the extra cost. I've had a few diamond-tipped bits going on more than 30 years, and they still work for drilling holes in glass (I'm a part-time stained glass artist). Carbide tips are too soft for glass and most porcelain.