Old platypus fits well, that's the ones that are squared off, not curved. Not sure if there is a middle generation I missed that might also fit, but the new ones do NOT fit, not with any washers I tested, thin, thick.
However, I did note one thing a few weeks ago on a trip, you really do not need to squeeze very much, just start the thing going, then you can let it go without any further squeezing until the dirty bag is dry, so that might make the sawyer bags last longer. Personally I skipped them, and used old 1 L platypus and I also brought a 2L evernew which I ended up never using, didn't need it.
I also got the adaptor for the clean water end of the sawyer, and put a short 4" or so length of tubing on that, made it easy to fill the bottles.
I would give the sawyer two thumbs up, best new product I've used in years, only reason I'll ever bring any AM is as an emergency backup.
Still have to work out a decent prefilter system, probably will go with the method someone here recommended, cut metal coffee filter crammed into dirty water end.
But this filter is so nice to use, and will gravity filter after you start it, goes slower, but works totally fine.