I would like to know how to go about dealing with non muslims entering the house for eg plumbers. They are always dealing with wetness. Names and appearances strongly suggest they are non ahle kitab. Is it necessary to make all the areas pak? They are sent by the building maintenance so we don't really have a choice on them.

Ahle Kitab is preferred in this case. However, since this is not a choice, make sure the place is throughout cleaned and dried after they are done with their work.