Use a screen, a sieve, or anything that will allow the water to pass through and will fit in the toilet.

personally, I don't use a strainer--it makes the whole flushing experience so gross to me that I would otherwise not do it.

I don't really see a need, anyway, since the stones always float, and the pre-flush exercises leave your bowel so clean that you'll pretty much just see stones and maybe some other loose gunk that falls to the bottom.

Unless I'm missing something...does anyone know that some stones sink?