Had to drain the tank -- pulled the hose off the carb, stuck it into the nozzle of my 5 gal jerry can (perfect height match!) and switched to prime.  Many minutes later it had stopped running, so I pulled the gasoline valve off to remove the tank (so much easier) and no more than a quarter tsp of gasoline dribble out.

Someone asked, the answer is:

PRI gets right to the bottom of the tank.

The most logical reason for that is so you can prime the carb when starting after running out of fuel using ON/RUN.