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www.garagejournal.com another site ran by Ryan. There are guys over there that have a ton of information on compressors and piping systems. With that said i would remove the plug in the tank after you relief the pressure. Then install an automatic tank drain. I shut my compressor down for the night but leave the auto drain plugged in and let the compressor drain down that way for the night. Gets rid of all the moisture in the tank before you start the next time working.