Taped off the now-open fittings on the tank at both ends of the sight tube and the vent tube with self-fusing silicone tape. Set the tank on blocks so the outlet wouldn't touch anything and filled it up. Came back a while later and put the plug in and tilted the tank plug-end down to see if there was any leak along the upper front end where I thought fuel was coming from. No leaks at all. So I let the water back out. So where did fuel come from, just as I reached the 13th gallon? My theory is I had filled fuel to the bottom of the filler neck, and it started to spill over. I was filling with the tailwheel propped up, and stopped the fuel loss by putting the tailwheel back down. I didn't think to check that the level of the bottom of the fill opening had been reached. This makes sense. The plane will be filled tailwheel down then the plug installed so this won't be an issue. Was it worth taking the tank out to figure this out? You bet! Leaking fuel is not something to discover in flight.
