I know you know but:
Screw your 20oz or whatever to the ASA. Open the on/off then open the front handle, this dumps the remaining Co2 from your bottle and chills it down, giving you more of a fill when you fill it. You can hold yourbottle under the dumping Co2 flow to chill some more. Then close the front handle and open the back one up, tilt your bottle about and listen to the noise as it fills. When this stops, close the back handle, turn your bottle off, open the front dump, then unscrew your bottle.
Gaz