As a newcomer to the hobby I wonder if anyone can help/ I have a machine mart/Clarke Bodyshop Filter / Regulator - AN3. I should like to know how to take it apart to clean the filter. it has a large knurled nut holding the gauge to the body but I cant turn it. Also there is some sort of (I assume) drain off tube at the bottom, with a small knurled nut which again I cant undo. Is this to drain water out?