Are there any private washrooms, i.e. a sink and toilet in a locked room together, in lecture buildings on campus?

Maybe the ones for wheelchair people, they are usually for 1 person. Not sure if they lock or not.

Depends upon the building? I know that ITB has them, for instance, in the "ab" part of the building.

You can probably find them best using this site: http://www.mcmaster.ca/uts/maps/. It gives detailed maps of all the buildings.