What should one do when done sumping a small amount of fuel during a pre-flight? Should it be dumped on the ramp? Or is it considered necessary to find the container far away from the airplane? Is it considered safe to dump it right back into the plane if it is uncontaminated?
The FAA issued an Aviation Safety Program publication called All About Fuel which talks about fuel preflight, including sumping fuel. It contains the following:
Preflight Action As pilot in command, you have the responsibility to determine that your aircraft is properly serviced. Check your aircraft before each flight and be sure you have the correct type of fuel. This practice may save your life! Take the time to inspect your aircraft thoroughly. Good preflight procedures:
- Be sure all of the fuel and oil tank caps and covers are installed and secured properly after you visually check the fluid level.
- Observe the color and odor of the fuel as you check the tank.
- Draw a generous sample of fuel from each sump and screen drain into a transparent container. Check for the presence of water, dirt, rust or other contaminants. Unless you have the proper kind of fuel tester (e.g., GATS jar with intact fuel strainer), do not attempt to save the fuel drained from the sumps by pouring it back into the tank. Note: If you are not equipped to safely pour the drained fuel back into the tank, please be sure to dispose of it in accordance with EPA regulation.
- Check that each fuel tank vent is clear of restrictions; i.e., dirt, ice, snow, bent or pinched tubes, etc.
Any FBO that sells fuel should have a way to dispose of it. Some of them make it more obvious than others by putting sump barrels out on the ramp, but ask them what to do with it before you go out to the airplane and they should be able to help you out. For environmental reasons, you definitely shouldn't dump it on the ground, because even if it does evaporate, it will come down somewhere. At some airports you can even get in a lot of trouble (and have to pay a big fine) by dumping fuel on the ramp. Don't take a chance!
You should dispose of it in a fuel disposal container, if your airport has them (and many states require it). Barring that, the best option is a type of fuel strainer called a GATS jar that has a built-in filter to catch any particulates. If you pull a sample in a GATS jar that comes back "dry" you just unscrew the filter and put it back in the tank.
If you pull water, you should dispose of it in a way that doesn't involve dumping it on the ground. Either put it in a disposal container (lobby your airport or FBO to install them if they don't exist) or your own labeled gas can and use it for your lawnmower or something.
If you have no other option, try to avoid pouring it in a puddle on the ground. Toss it in an arc so it covers a large area and can evaporate as quickly as possible
I always put it back in the tank if it's not contaminated. Even if it is I'll put as much as I can back in. A few millimeters of water is not going to do anything when it would take almost a gallon of it just to reach the fuel pickup.
As for dumping, I've heard the EPA has been known to watch airports with heavy flight activity. They'll write your tail number down and send you a fine. Some states don't have any laws about it, though. I would save all the fuel I could, honestly. You can filter out uncontaminated fuel and reuse it. I know that's not really plausible if you're not in a hangar, though.