Greese from Mechanic distroying other tenants clothes in new washer

[Ben S.]

I've had a tenant in a 4-plex who has his laundry destroyed with grease all over his clothes. We suspected it was from another tenant who was a mechanic and I warned them that they needed to stop washing his work clothes in the washer but we are on occurrence #4 now what should I do?  I installed a brand new speed queen washer that cost over 2,000 to make sure it wasn't the washer causing the grease and here we are with the same issue.

Should I give them a fine?  

Should I have them buy new clothes for the tenant who lost clothes because of it?

Should I ban them from using the machines?

They claim they have been washing his work clothes at their parents but obviously that's not actually happening...