Had toilet and sink put into cuboard under stairs a few weeks ago(1945 semi). Backs onto garage but waste pipe goes under kitchen floor out to soil pipe on back of house. Extractor fan operated with pull cord. All tiled, nice job. Toilet only used 1-2 times per day at most. Flush works fine, no blockages
Only big problem is a very odd smell in the cloakroom. Does not smell of waste / sewerage but still very strange. I can only describe it as a sort of acrid smell. Partner thinks is smells slightly like fume / gas (no gas pipes nearby). Everyone notices it but nobody can pinpoint what it could be. No sign of dampness.
Plumbers are coming out this to look again, Pipe at back of toilet into floor is not solid, white flexible (looks like vent hose you use on a tumble drier). There is a gap where this goes into the floor, I think they are going to seal around this, in case smell coming from dead mouse under floorboard, they said. Smell was also in the hall but mainly confined to the cloakroom now (extractor fan helps !)
Is it possible to get methane build up from work like this ? Any suggestions welcome. Have not paid plumbers final payment yet.