Rarely you will find a plumber who knows what is he doing, however the way thing works under the circumstances is that YOU should know what you need and go to the hardware store and buy the hardware and lease a plumber from there it self.

However On a serious note, it is suggested to speak to the owner of the building as they know the ins and outs and they can at least refer to someone who MIGHT have worked on this place before.

For the matter some owners might charge you or hold your advance deposit if they find out changes or tampering in the leased/rented accomodation.

All the best