Originally Posted by
TheOddOne
I teach NOT to put fuel back in the tank - it's considered contaminated, even if it looks OK.
...
I DO teach spill it onto concrete (not asphalt as it melts it) and watch it evaporate. If it's all water, it can still smell of AVGAS and have a blue tinge, but the evaporation test is positive for fuel. We've had one tank on our PA28 annoyingly have remnants of water contamination (admittedly only small globules of water) after being left out in the rain at maintenance.
Also, as above, it's a waste of time doing drain checks unless the aircraft has been stationary for at least a couple of hours, as the contaminant will be in suspension. Fortunately, our AVGAS supply at the airfield has a good filtration system and is checked daily.
We do our drain checks in the hangar, before moving the aircraft, at the start of the day.
TOO
In the US, if you dump Avgas onto the ground you will get a big fine, and maybe lose access to the airport. GATS jars are very efficient at separating water, and the gas you put back into the tank is the same gas you just tested, so how is it contaminated? Water separates from Avgas in about 10 minutes. Not everyone has a hangar.