Well, iv been doing this for a while know and its a awsome thing to do.

First, get a ziplock back, or any clear plastic back that is waterproof seal.

Second: Find some porn you like, print out the pictures.
Then, put the porn you like into the ziplock bag. -you may need to cut of some the paper to put it in the bag-.

Finaly, when your ready, take the bag into the shower, and masturbate untill you expserince a awsome orgasm. With no mess to clean up!