The Bullet.
I noticed this even though I use a vacuum cleaner to try draw off any waste at the door. Tipping the Bullet 2 and tapping the front legs to a surface ejects some of it, maybe all of it I have know idea. The legs are not designed to do this so be gentle if you try this. That is unless someone has another method. Shaking tipped down to the front works too but the R2 is a bit heavy.