craftgrrl | Decorating ceramic tiles

(Apologies in advance if this has been covered before and is hiding out in the memories, but I did have a wee look beforehand.)

I'm planning on doing a mural of sorts on the tiles over a bath.Right now they're bog-standard white ceramic bathroom tiles, with dirty grout (if that's what it's called, not too up on my tile lingo here).

Before I go ahead with this and it all peels off the first time someone splashes it with soapy water, are there things I should be taking into account, such as:

+ Fancy waterproof, extra-strong paints, or can I use something cheaper (presumably not water based though?) and then coat it in a hard-wearing protective varnish or similar?

+Can I use paints not designed for tiles to create different effects/surfaces?

+ Will I need to use a primer or something like that to start with?

+ Are transfers totally out of the question? (once upon a time I transfered pictures onto some canvas chuck-like shoes using acrylic gel medium and aside from going cloudywhite when I walked through puddles, the images stayed put, but perhaps that's because it could soak into the canvas a little bit, which might not happen on slidy tile-surfaces) I'm sure I *did* read a little about this in the memories, but what I need to know is if these surface will stand up to potentially heavy use/coatings of bubble bath and assorted gloop)

Thanks very much! I will let you know how this works out.