Sand is a good option, since it compacts, and poop stays on top of it, and is easily siphoned off.
I keep barebottom tanks with my goldfish, quarantine tanks, and generally anything that isn't a planted tank. I hate vacuuming gravel, but I hate nitrAtes more, so I just opt to not have gravel at all.
The poop is sucked up by the filter intakes. I have goldfish, so there is typically 10x the tank's volume (or more) running through the filter every hour. Everyone that sees it thinks it looks amazing, and artistic. I also use driftwood, rocks, and potted plants to keep it from looking bear.