In our local tower they pee in the sink (or so they say). I'm not sure what they do when they have other needs, but I didn't really want to know.

The *real* reason for having a sink in the tower cab : )

When I worked in ops at a regional airport the AM controller opening
the tower didn't get a bathroom break until the next controller came
on. On a few occasions I watched the radios for him while he answered
nature's call.