I finally decided I'd have a go at it, flying to Oshkosh in my (Rusty's, Richard Nadig's, mine) RV-3B.

I still hadn't put the facet transfer pump back in that Richard had removed (and per archives, Rusty had a hard time getting it to work properly). I figured I could use rudder to make sure that fuel would flow from the proper tank. Not so. I saw the fuel gauge on the right tank go down to zero and had 6 to 8 gallons left in the left tank but could just not get it to drain into the right tank no matter how much I stepped on the rudder. Even tried circling to the right. Just as I had decided I'd better land and was looking up airport info, the engine quit. Fortunately I was at 8 or 9,000' feet and made an uneventful landing at the nearby airport (4A4). Saw about 1,000 fpm descent at 95 to 100 mph with stopped prop. Topped up both tanks and returned to Shady Bend. I could probably have made it to Oshkosh using more frequent fuel stops. But I was worried about having damaged the fuel pumps. I don't know exactly how long I let them run dry, could be as much as a couple of minutes. Didn't want to press my luck and returned home. This time the tanks drained equally (with a nudge of rudder input). Go figure!

Situation was compounded by the fact that my fuel flow calibration appears to be off.

Or the tanks are leaking gas when near full. While flying and looking at the wings I saw some moisture (drops) sitting at the front lip of the fuel caps. O-rings appear to seal OK, but I guess there could be a leak between the tank skins and the rings riveted onto them.

Looking at actual fuel used flying back to Shady Bend, it comes to an average of about 8.5 GPH.
Fuel flow most of time indicated 6 GPH. I had calibrated the EM2 over more than a hundred gallons of gas used, but never been flying with full tanks when I did that.

Anybody with similar experiences that can shed some light on this (tanks loosing fuel)?

And just to reiterate: you cannot safely T tanks together on a low wing aircraft and no fuel selector valve!

Finn

(I don't think I beat Ed's longest glide record.)