OK a drain type smell coming from a downstairs loo.There is just a toilet and wash hand basin in this two storey mid-terrace house. The "room" is located off the hallway and to the front of the house. There is a small drain directly outside but it is not blocked or smelling at all. It doesn't seem to be coming from the toilet bowl or the sink. The floor is tiled (ceramic floor tiles)..there is a small window which when opened takes it away but builds up again on closing it. The other upstairs en-suite and sep bathroom is perfect. A plumber checked the loo and said it was fine.
Any ideas?
Any ideas?