I put 2 gallons in each tank and then pumped out what I could with the airplane in it's flight attitude. Once this was completed, I then calibrated my tanks is 1 gallons increments to 10 gallons and then every 2 gallons after that.
Flew on the left tank until the engine started coughing in cruise flight (over an airport).
Then landed and took the fuel drain out. I got less than 1 cup of fuel out of the tank.
I was not trying to get every last bit out by slipping or holding that wing high. I was very impressed with how little fuel was left.