You can get what is essentially washable astroturf from various pet stores. I've not bothered with it because I figure my little ones will just find a way to get under it. I use newspaper and Carefresh but they still seem to go on the glass half the time. I've resigned myself to scrubbing the tank every other feeding since that's when they're out of the tank anyway.

Larger snakes seem to be better about pooping on the newspaper or carefresh but I still have to scrub occasionally.

They're all prone to soiling their water, so keep an eye on that too.