[J57ltr]

Personally I always leave them full. I already paid to compress it why let it out. That goes for our 80 gallon shop compressor as well. Drain the water out of it by all means, but no point wasting your time filling it back up. I have a 1 gallon compressor for a brad nail gun at home and I fill a 5 gallon tank and keep them both full. We also use a dryer at work because the desiccant style dryers only work for a day or so before you have to remove the desiccant and cook the moisture out of it. We bought it at harbor freight too and it’s worked great for the last 5 years. It’s way too big for your application, but you might want to check on the ones that mount right before the gun.

BTW if you are talking about the little ring you pull and it releases air, that's a pressure relief valve it's there in case the pressure goes too high.

Jeff