The "bottom" never gets pumped at a gas station. The pipe which draws fuel out of the tank is suspended above the bottom; there will be anywhere from 4" to 6" of gas remaining in the tank when the station runs out of gas. That's to collect water at the bottom of the tank where it can be removed and the stations and delivery trucks have tank dipsticks and a water-detecting paste to tell if how much water has collected.
There would have to be that amount of 'solids' for it to get into the pump lines at the station, where the pump filter would have stopped it, just like the mower's filter did.
Should have clogged and stopped.
More than one station operator down here has been done by the Standards Association because when they come to do a random pump volume check they find all sorts of contaminants in the fuel and in many cases the filter elements missing.
The cut the stations make is around 20¢ / gallon and filter elements cost near a grand to buy and almost the same to dispose of ( contaminated waste ) .
Older stations that are not hooked up to the refinery electronically are renown for buying "fuel" from unknown truck drivers cash, nudge nudge wink wink.
More than one truck driver has been done for picking up waste solvents that never seem to have arrived at the appropriate waste station or reprocessing depot.
Any guess where they end up?
Times are tight, things are tough, I have a lease payment coming up that I can not meet and some one offers me 2,000 gallons "reject fuel " for 50¢ a gallon.