It breaks down the waste and paper. Both of which stick to the sensors AND it liquefies it so dumping is fast and clump clogging free. Chems have been around for years for marine and RV. There IS a reason it is used.
And YES it smells without chems. Sady, Many CG's do not require a donut or screwed in elbow when dumping at the site. IT SMELLS all over the CG when campers dump a tank without chems into an open sewer hookup.
Not a one of you who do not use chems can say you can stand right over that sewage hose while you are dumping without gagging,and say the sewer gas doesn't stink up the air.
And inside? The toilet is NOT your residential toilet plumbing there is NO us shaped p-trap to stop sewage gas. Every time you step on the pedal to flush it is OPEN directly right straight to the tank and all that untreated sewage smell and bacteria emits right into your RV. There is NO p-trap. Just let it fill up sometime if you don't believe it, and shine a flash light down the toilet opening and you will see raw sewage floating around right up to the toilet
I will not help a fellow camper or show a fellow new camper how to dump if they have not added chems to the black tank. The stench is not worth my time or health to help.
Just RV once in the southern states and god forbid during their summers you WILL smell your untreated black tank which is sitting outside acquiring the ambient temps of over 98 degrees just boiling that sewage. Then step on the toilet pedal to flush and open it right up to your tank and all your untreated sewage, and get back to us. :W