I am going to disagree... been flying for a while.. I noticed how grungy my fuel looked as I pumped the unused Glow fuel back into the one gallon jug. By the time I used up the gallon of fuel and got to the bottom of the jug, the "new" fuel was really dirty...

Currently, as the engine runs the black carbon from the engine exhaust is being blown from the muffler back into the tank to pressurize it. This black carbon is a potential source of engine wear in my thinking. Combining this fuel with black carbon in it with my pristine new fuel was abhorrent to me.

My solution is to pump all the unused fuel out of the airplane's tank at the end of the day into a separate "used fuel" container. Next flying day, I pump the "used fuel" back into the airplane's fuel tank and then switch to new fuel to top off the tank. This way, I am using up the "bad" fuel as I go and my fresh fuel always looks brand new. The "bad fuel" never gets as dark as the old method. How can that not be better? I am never running fuel that looks as bad as when pumping the unused fuel back into the new fuel container.

It works for me..