The scum is from E-10 fuel gone bad, best to use non ethanol. All I use cept for the Jeep, even then I use a conditioner.
No disrespect meant, but this sounds like a ridiculous level of paranoia to someone who has spent a couple of decades living in states where non-E10 is almost impossible to get so it's all just about everyone uses in everything around here.
The scum is from FUEL gone bad, even the non-E10 will leave deposits if left long enough.
Yeah yeah, I think E10 is probably even worse in storage, but it still takes time.
There's no need for conditioner unless something is going to sit for more than just a few weeks at a time.
I say this because of our cars, our bikes, and our boats...and everyone else's in much of the northeast.