I used to when buying brand new compressors/tanks, would open it at the top, drop in some solvent slosh it around, drain it out and after a decent amount of dry time follow that with some (pint?) quality paint, and slosh that around and quickly drain, the idea is to give some protection to the bare metal inside where water would constantly collect daily.
I now have an aftercooler right after the compressor, that has a fan on the same circuit that runs with the compressor. Aftercooler next feeds a water trap with an auto drain. Being in Florida I am still amazed how much water still gets into the 80 gal tank.
I am not fond of depressuring the air system down to zero at the end of the day every day for no real purpose. It pressure cycles everything just accelerating eventual fatigue failure at the weakest link in the design.
