How often do you drain your air compressor?

I drain my 80 gallon tanks before startup especially if I am going to blast or paint something. All of my tanks have a 3/8" pipe with manual operation ball type on the bottom drain valve
set up on each tank as I run multiple 80 gallon tanks in series for sheer volume. Manual operation valves either show you your drain port is open or clogged.....NO Guessing! You should never wait
very long especially if you live in a high humidity prone area of the world........ Some old craftsman (Sears) tanks do not have a bottom drain valve but do have blocked off ports on top of the tank......This type of situation calls for a quill drain system which can drain a tank (90-95%) even sitting in the upright position by pressurization of the tank.
A air tank not drained 1/2 filled with a liquid level can be very dangerous and can explode as the pressure wants to go somewhere and we all know water is a solid and does not compress.