Dawn is probably the "most gentle thing that works". Simple Green may work better and is also non toxic but is also $$ compared to Dawn. MSDS on Simple Green says eye irritant, so does Dawn. Johnsons Baby Shampoo may be more gentle (not eye irritant) but may not work as good.
Totally agree, however I don't know the ingredients (chemical composition) of "undercoating". It's more that just tar, I think there are some epoxies in there???
