BRS posting: The cup quickly gets clogged. I keep my hatchery next to my reef tank and the little cup doesn't drain much so when I transfer the bs to the tank it leaks all over.
Cleaning doesn't seem to help. So, I 3D printed up my own little cup, with no screen in the bottom (I don't mind transferring the saltwater with the bs). And it works great now! I you want the STL file to print your own: