How often do you drain your air compressor?

My quincy came with what I think they call an aftercooler. Its a big radiator on the output of the compressor. It must work because I get pretty much zero water in my air lines. It all condenses and drops back in the tank so it never hits the air line. I cant say enough about this compressor, its truly awesome in every way.
I had originally planned on buying a refrigerated dryer for it but never had the need. I use it mainly for sandblasting and sometimes I blast for 4 hours straight.
Those homemade condensers work great. It would be even better with an automatic drain on it.