I want to purchase a Lease on a property which is a ground floor flat but when I viewed it I noticed wallpaper had peeled in the bottom corner up to about 18 inches and there was black (dry) residue on the paper. The property has been empty for about a year now. Immediately outside this area there is a downpipe from the guttering and it is going into the drain and is not broken. My question is: could it be a collapsed or blocked drain that would cause this or worse scenario it’s the DPC which has breached?