With some machines...
Namely, my Hoover Windtunnel 2 Rewind Pet and Bissell C4 Cyclonic canister vacuum, both have crappy dust bin designs that allow the dirt to get stuck in them and not come out when you open the bottom door. This necessitates lots of tapping to dislodge the debris, or pulling it out by hand. The constant tapping causes dust to collect on the outside of the bin, and then it has to be wiped down afterward.
On some machines, such as the Dyson DC07 and Eureka AirSpeed Unlimited Rewind, those bins are also bottom-empty mechanisms, but both are designed so that everything falls out when you open the bottom door. I prefer those kinds of dust cups, where there is no "lip" to trap debris.
