I HATE cleaning my 22" WSM. I always forget post cook and have to get to it the next day. Seems lately I have to wait until it stops raining then dump out the gallon or two of water in the bottom along with the ashes. The water usually backs up and out the bottom vents and then the lower grate and charcoal ring are sitting in water too. Great design weber 
I also try to leave all vents open and some ashes in the bottom even when the cover is on. The ashes seem to soak up any moisture and keep the fuzzies away between uses in my past experiences.
What are your thoughts about drill an 1/8" hole right in the middle of the bottom? Possibly align it with the hole in the heat shield?

I also try to leave all vents open and some ashes in the bottom even when the cover is on. The ashes seem to soak up any moisture and keep the fuzzies away between uses in my past experiences.
What are your thoughts about drill an 1/8" hole right in the middle of the bottom? Possibly align it with the hole in the heat shield?