One would hope that they didn’t have a sign saying Muslims Only” and that anyone could wash their feet in the foot bath.
Most large buildings have the necessary facilities already in place. It's called a "janitor closet". Inside is a handy device called a service sink. It's where mops are cleaned, and washbuckets emptied. It looks a lot like a mooslim footbath, and is very handy for janitors, too. It's also a whole lot cheaper than a gold-plated footbath.