It depends on different things though, if you are very tight than you must stretch your whole otherwise your pain will be to unbearable. Lube and try different brushes. And to the question if it hurts... well it actually should hurt. That is the whole point of a brush inside you. If it didn't than you could just take a normal dildo. Pain is good and necessary for women if they want to be subordinates or slaves to their master.
depending on the brush (i have used a few different types), they can be quite uncomfortable but then it cums down to if you like that sort of thing. besides a bit of lube, no prep
Next time: a toilet brush