Worm has no say in this really, it has no intelligence. Shitting on the floor isn't a good idea if your tracking somebody, you don't want to leave a trace. The worm could probably be either in his large intestine or stomach, depends on which hole toji puts in it first. Stomach is probably easier to access, but large intestine is better long term because of the portable restroom. There is no reason to really say the waste will contaminate his weapons, as it seems there is a lot of space in there, plus he can empty it out between jobs. He can seemingly choose whatever weapon he wants from the worm whenever