How can I make the landlord fix the sink and the washer which causes the growth of mold and fungi?

When we moved into the apartment, the sink where the washer would rinse into would always over flow. We were concerned about the moisture seeping into the floor. We brought this up with the landlord. He placed a dehumidifier but did not fix the problem. This was in November.Now, there is Domicile Cup fungus growing right under the sink. The area around it is wet to the touch. My concern is that if we contact the landlord, he will just "quick fix" the problem and probably just remove the fungus instead of fixing the sink. What options do I have to make sure he completely solve the problem.