You have not told us anything about the present lease term. If this is a month-to-month tenancy and the unit is not rent-controlled, the landlord can increase the rent on one rental period's notice. Is this a month-to-month tenancy, or is this a lease for a term that has not yet expired?

You can try having the plumber document for you that the plumbing problems were caused by ordinary build-up over time, not by anything out-of-the-ordinary that you introduced to the plumbing, such that the clean-out would constitute ordinary wear-and-tear. Once that is documented to the landlord, you can ask him to reimburse the expense and see what he says.