In a word, no. Drain the tanks first and you will have less mess. Leave the side panel open when you are done, and just add a little fuel back in first for a leak check, just in case.
Check my post in the Sick bay as to the old imperial valves in my PA12?
Any comments?
Seems that the valves have been pulled from Univair. According to rumor these were the same valve that were in "John Denvers" airplane that he crashed while fiddling with the valves.