Last year our tenants complained about black mould on the walls. We immediately contacted a plumber to find the source of the damp. He said it was because the tenants had blocked the vents and were using a dryer daily. He told us to tell the tenants to use the dryer properly (they were not emptying the water), use the fan above the cooker, unblock the vents and open windows occasionally. The mould keeps returning. We got a second professional opinion which agreed with the plumber. The tenants refuse to take responsibility and say the house is affecting their health. They have been given notice according to RTB guidelines. Any advice on how to deal with this in the meantime?