Hi... 1st time poster; long time lurker here....
So I inherited a air compressor (1HP Speedaire), and 1 of the things it needed was a new drain c*ck (the old one somehow busted off). Upon getting the remining nipple out with a handydandy screw extractor, I could see that there was some gunky greasy stuff at the bottom of the tank. How much?? Idunno and being only a 30 gal or so tank, there're no inspection plugs to peek into.
So the answer is: A) "Thats normal, and as you should have a filter on the output side of things, theres nothing to worry about"
B) "Rinse the tank out with (kerosene?? mineral spirits??) a time or 2.
C) (other)
Thank's in advance, Mike G