Thick black mould everywhere!!!!!!HELP URGENT

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It seems to me that you and various professional third parties that you have consulted, have given you the answers to your dilemma. The tenant is clearly at fault, and they should foot the bill for any clear-up caused by the way they live. The Cannabis farm next door is a red herring, I believe. With five kids in the house they need to dry their vast wardrobe of clothes somewhere and I suspect that the radiators and banisters are the obvious cheap dryer for them. If they kept the property clean and ventilated correctly then surely the black mould would not have built up to that extent. Get them to ventilate the property properly and to use a tumble dryer that is ventilated to the outside. And inspect the property more often to see how things are going. Surprise visits by you are sure to uncover the truth about their behavior. Don't rehouse or replace any clothing until they PROVE that you're property alone is at fault.
Regards,
Mr Meerkat