Gas chambers are widely used for sterilising materials going into clean rooms for compounding of medicines. While this does meet the definition of “one more thing”, it is rather an important one.
With showerheads?
Not that I've seen. Nothing about the phrase "gas chamber" to anyone knowledgeable about pharmaceutical equipment suggests shower heads though - it's a simple case of you attempting to move the goalposts to support a bad argument.
"Gas chambers are just a tool"
But a tool that has very few uses besides large scale genocide. So of course it would be ridiculous to argue the gaschambers are just a tool, because they are (A) the result of an engineering project that tried to kill as many people as possible in a short time, without using valuable war resources like amunition, so the "tool" cannot be isolated from the context of it's creation, and (B) there is one thing gas chambers are good at and it is mechanizing genocide. One could potentially come up with other things they could be used for, but there is just the one thing theyr really excell at.
Computers have more uses, but they are "not just a tool" either, because in reality nothing is.