Black Tank Build-up

We had a severe buildup problem in our black tank last summer due to an excessive amount of ABS glue used at the factory. Tried all sorts of methods and nothing worked. The only thing that did was liquid drain cleaner, the kind that does not attack metal or plastic in an RV tank. It ended up looking brand new. Can't recall if it said septic safe, but I wouldn't dump either type into an on-site septic disposal system because it can destroy the disposal field. Dump only in a municipal sewer system. If nothing else works, this may be an option and should work with warm water plus the chemical reaction generates heat but I don't think it would freeze with that stuff in the water anyway. You'd want to stir the water around a bit somehow, maybe with an old length of garden hose?

The standard RV chemical tank cleaners need to be used at 70 degrees F (or thereabouts) or warmer and you need to travel a bit for the water to slosh around.