OK, full disclosure here since you?ve hit on a sensitive topic that has caused an awful lot of frustration and embarrassment.
My RV-12 was down for maintenance, SB upgrades, and paint for over a year, finally getting it back in the air last August. Looking back, I did almost everything wrong with regard to refueling. Metal 5-gallon gas cans sat empty for 18 months. 93 octane ethanol free gas was purchased from a rural gas station that didn?t sell much gas. No filtration was used as this filth was poured into the empty tank. Within no time at all, my gascolator samples were full of enough debris to entirely cover the bottom of the sample tube. The gascolator screen was packed and fine debris made its way to the carb bowls.
With an attitude of total denial regarding the seriousness of this problem, and a refusal to remove the fuel tank again, I disconnected the fuel line from the gascolator to the engine and began pumping fuel from the tank through the gascolator into clean plastic cans. The flawed logic was that I could flush out the debris from the tank, check it with the gascolator samples, and pour the same fuel back into the tank through a Mr. Funnel. This foolishness went on for days as I wore out the fuel pumping, filtering, and sampling. The gascolator just refused to clear up.
Finally after serious some soul searching, I stopped the charade, removed thank, and opened it up by cutting off the circular access panel. What I found inside made me almost physically sick. The entire tank interior was absolutely covered with a fine grayish brown powder with a few larger particles. I spent a couple of hours scrubbing out the tank with hot soapy water and a rag. After drying the tank with a towel and airing it out in the hot sun for a few days, I re-installed it, plumbed everything up, and tentatively poured 5 gallons of fresh fuel from a better gas station using brand new plastic cans and a Mr. Funnel. More flushing and sampling cleared up any residual debris in the lines. Carb bowls and gascolator were also checked repeatedly and cleared up completely.
The takeaway from this harrowing experience:
1. Buy clean fuel from a source that sells a good volume.
2. Use only clean non-metallic fuel cans.
3. Run EVERYTHING through a Mr. Filter or equivalent.
4. Sample your Gascolator before EVERY flight.