I'm going to keg for the first time soon (hopefully tonight) and in preparation I replaced the o-rings around the dip tubes and thoroughly cleaned the keg. I then filled it about 2.5 gallons of starsan and sealed it up. Today I decided to make sure the keg was holding pressure before I put all the beer in it, so I pressurized it to 20 psi and then turned off the gas. When I came back a couple hours later, the pressure was down to 18ish. At first I thought I had a small leak somewhere, but after going over everything a few times I suddenly realized that it might be carbonating the sanitizer.
Any thoughts? Would the psi drop be that quick? The keg is at room temp. Should I drain the keg before I try to figure out if it's holding pressure so that carbonation doesn't come into play, or does it not matter?