A trick that works for me most of the time - Fill the bath tub just a few inches, with water just a touch on the cool side... About the temp you would bath a baby in, (what's the word? Lukewarm? but err on cooler I'd think) And if the water isn't good they'll you know by violent thrashing.
After a moment it should stick it's tail up and leave you a floater... But I've had a few times after two weeks no poop and the bath trick didn't work - but a few days longer and I cage ploop left behind for him.
Intersting side story - Me and my Girlfriend were playing with Icepick and suddenly she started gaping her vent... At first we thought perhaps she was smelling our new Caramel male who was also being held and it initiated a mating response on her part... But before it was too late I stepped in and placed a towel under her and we both had an indepth look at a large fecal deposit being literlly shot out. And man oh man, given the chance they CAN project that stuff!
Gross as it was, it WAS a learning experiance! 8-P Lucky, no stinky clothes!
GL!