Soda. It foams up and you can try to clear your drains with it.
The really dangerous one is chlorine bleach plus ammonia. Emits a toxic fume. Never use bleach to clean up a basement floor full of kitty pee.
Only toxic if you are the Creature From the Black Lagoon. For those without gills it's more irritating (Chloramine is used as a disinfectant). For the toxic chlorine you need an acid.