I clean my bowl about once a month when im using it alot. In my experience the best way to clean them is with efferdent. its a denture cleaner. I fill a little container with hot water then drop one and a half in and they dissolve into the water turning it blue, then drop in the bowl and shake it every few minutes for about a hour. you should see the resin just fall off. Anything that stays in the bowl can easily be cleaned with a paper towel. That shit melts the resin away.

oh and by the way, you can strain the water through a coffee filter & keep your resin if you want.