A few evenings back after some painting was done, I decided to drain my compressor tank and let the filter in the water trap also get some air. I removed the clear water bowl and unscrewed whatever that thing is that holds the filter in place. The next evening I put everything back together and suddenly the regulator is leaking and the knob is loose. What the hell happened over night. Not in the mood to fight this thing, I got out my spare regulator and attached it. It only took about 15 minutes to do. Moving everything back in place I see the little plunger on the rag I have underneath draining valve. Could this be the problem. Very happily I undid all I did, put the plunger back in and it works 100% again. It's the first time that that little thing fell out but I'm glad it was when I had time and the spares to calmly sort it out.