What is the proper procedure for flushing out the air tanks after changing out the air compressor to get rid of oil in the wet tank?
It's a wet tank, you will never get rid of fluids out of it. That is why it's a wet tank. In my day you open the valves overnight let them drain, every night she is parked for the night. By morning that tank is ready to collect today's fluids.
Bet most don't know that you have to bleed the air out to get the moisture build up out... I did mine weekly... wintertime the moisture will freeze the airlines...