After all this time, I've forgotten which are septic friendly (peat tank). I'm going to check this out. EDIT: Googling found this: https://www.dirtrider.com/tests/parts-accessories/141_1011_easy_wash_air_filter_treatments_review/ Quote-keep in mind this article is from 2010. It sounds pretty nice though, with the new oil (Green bottle). No Toil Evolution https://notoil.com/no-toil-classic-evolution-oil/ **looks out of stock 02/2021 $8.95 16 oz/$34.95 1/2 gal./ $19.95 Evolution 3-pack (oil, cleaner, rim grease) What's Hot Evolution, now green, replaces the older red No Toil we were very fond of. It has an aqueous carrier agent to replace the isopropyl alcohol, which addresses concerns about shipping regulations, wrecking filter foam and especially glue degradation. It does not make the filter expand when applied, and if left in for long periods (over three months), does not stick the filter to the cage or air intake boot. Cleaning is much better than standard oils. With the No Toil cleaner and warm water the filter comes out pretty spotless. The only nontoxic, biodegradable filter oil. What's Not Sometimes a little goo remains after a second cleansing, and if regular oil gets on the filter (say from an engine vent routed into the airbox), it does not clean out with the No Toil cleaner. Spreads the best on a totally dry filter, does not like any remaining water during application. Takes a specific cleaner, other types won't work.