One of the best pieces of advice I got early on in my snake keeping days... this is guaranteed to make a snake urinate/defecate.

Put on your best outfit... pick up snake... VOILA!!! Elimination!

Or had the snake to your most uptight friend or relative (I prefer to use relatives myself). VOILA!!! Elimination.

Seriously... do not worry. The snake will pass fluids when it is time. If you see her/him drinking, then you are good.

Watch the paper... (if you're using paper)... it gets wrinkly looking... they pee a lot more than you know. If using a substrate such as aspen you will not see it as much.

But they can flood an enclosure... if the snake is on top of the hide.... I check for presents inside the hide.

Bruce