As seen in Dave Bonsall's Lecture. A hilarious gag! I've used this many times at bookings when the situation is right and with the right audience member, mainly if they're a heckler. If you've ever seen the Dave Bonsall Lecture, then you'll be well aware of this gag.
I tell the audience that it's a prediction toilet, use various methods to get them to think of a card and then get them to take a peek under the toilet seat - They then of course get squirted with a little water.
I've had whole tables giving me standing ovations with this excellent gag!