I worry about tipping any 4 stroke engine upside down as the oil in the sump will flood the top end and may cause other issues. I think a better approach is to siphon out as much fuel as possible and then start up the generator to clear the remaining dregs of fuel that siphoning didn't remove and then let it run until it runs completely out. Then full choke and pull the start cord a few more times until it stops coughing and you're good to go.
I run all my small engines (that are in intermittent use) out of fuel and I have never had any issues with starting them back up after months or years. Start on first pull every time with new fresh fuel. Removing the fuel will prevent cycling stale fuel into the carburetor. The additives in today's fuels have faster evaporation rates than in years' past and they will quickly foul up carburetors if run, or, if left in the carburetor bowl to turn bad and foul up the carb so that it won't start.