tile on tile

I have a customer who wants me to install pebble tile over the existing tile on her shower floor. I know that I can install tile over an existing surface but what about doing it in a wet area like a shower?

As long as the floor is dry I dont see a problem.

I believe someone makes an extension for the drain

I've done it dozens of times and here is the Extend O Drain. http://www.tools4flooring.com/extendodrain-338-in-kit-p-1024.html

Jaz