I've had one clog requiring mechanical assistance to clear, and one "stall" of a hot-dog (with bun) - sized poop, which cleared on its own, in the late part of the flush. Still, it beats the record of any other low-flow toilet I've ever had (except for the PA models). Flush is noisy, but only the final "glurp" as the trap clears. No problems with smears or marking. One frustration is the shape of the bowl makes it look dirty, even though it's clean, especially around the waterline. I think it's a light-and-shadow thing.