Fuel sumps are located in strategic areas in general aviation aircraft to test what’s inside. Usually, this is to look for water contamination or debris. It pays to check what’s inside. Twice I had to have the fuel drained. Once due to an endless stream of sediment. Another time for color and smell. It had the appearance of Jet-A which would never do in an engine that burned 100 low lead. It’s rare but not impossible for an inexperienced lineman to make an error in judgment when filling aircraft. Fueling mistakes have stopped hundreds of engines in flight so I always check what the engine is consuming. You wouldn’t want to eat something that you didn’t know in advance was acceptable (for now, I’ll exclude the topic of MRE’s). Neither does your airplane engine. It’s a lesson I learned long ago but not in a plane.
During my junior year at college I had the experience of sharing a house with four other guys. Not exactly animal house but we all had our habits. One of the guys would gobble up our grocery budget usually after returning home late at night despite our protests that food was to share. Another one of the guys, brave enough to cook, would prepare a bowl of chicken salad for everyone, only to find the bowl sitting empty in the refrigerator the next morning. We decided to make the next “salad” using cat food. Next morning the bowl was again in the fridge. Empty. True story, but we had nothing to do with his next culinary treat. At another time, the guy ate two cakes of activated yeast thinking it to be the same as brewers yeast (a health food supplement). It’s not. We watched in amazement as he began to ferment before our eyes. I’ve never seen anyone burp non stop for an hour.
So remember to check . You may be getting something you just don’t want.