We have just installed a bathroom in our loft conversion (2nd floor) and since then the bathroom on the first floor started smelling unbelievably bad. All I know is that they didn't put a soil pipe on the outside on the house but rather on the inside. The smell in the bathroom is coming from the shower only, not the tub or sinks. Our builder put One Shot drain cleaner in it which helped for one day only. The smell is so bad that it travels into the downstairs dining and living room, we can't even have guests over anymore without keeping the bathroom door firmly shut. Please help, this isn't normal and it severely devalues our house! Thanks