There was an article about this very subject in Britain at War a few years back. This is what I remember. RAF medium and heavy bombers had an Elsan chemical toilet in the rear fuselage. The Mosquito had a urinal system consisting of a tank under the pilot’s seat and a tube you could pee into so it was really just a urinal rather than a full toilet. The B29 had an Elsan type toilet in the rear fuselage. I don’t think the B17 had an Elsan. The only WW2 aircraft to have a flushing toilet was the Short Sunderland which had a compact WC originally designed for use in yachts.