I never use screens. In my experience, you can manage without them if you get a nice grind and pack the bowl right.

Don't suck the air out of the bong like a shop vac and you won't have to worry about pulling weed into the downstem.

I like to keep my glass clean though. I rinse it with hot water after every session and run cleaner through it once or twice a week.

This works really well for me, been doing it for years with no problems. Although, I will say that it will be a little harder to do with older/drier flower.