I'm looking to buy an additive that will dissolve any sludge in the pump (it's a Webster, with self-cleaning screen), as well as the tank and lines. I've noticed that some (such as the Hercules SludgeTreat, which I can buy locally) are mostly mineral spirits - plus a lesser amount of another solvent such as Glycol Ether EB. Could I just use mineral spirits?

Any comments in general about what additive should go into the tank? It's indoor, so I don't need any antifreeze component to it. I don't think I need a biocide, either.

Hercules Sludge Treat MSDS:

I've also been looking at this comparison chart by FuelRight:

(Beckett's FuelArmor doesn't score particularly high at 10 out of 30, but the Hercules SludgeTreat scores at 28.)