We recently had a very odd smell in the house, was like something had died and concentrated around the two bathrooms. It went, but in the last 2 days it has returned. Can't tell downstairs but upstairs it seems to come from the toilet, obviously I've done the whole cover it in bleach etc. but nothing seems to work. Downstairs is more tricky, I can't really tell where it is coming from. The upstairs bathroom is directly above the downstairs one, and in the past I've had mice get into the house in the downstairs bathroom (through a wall? No holes outside but they definitely get in halfway up the wall and into some light fixtures). So, any ideas? Can it be the drains if there is water in the u-bend? There is a drain under the bit where I'm sure the mice got in, could they have somehow got into the cavity wall from below and the smell is the drain under the house? But that wouldn't explain upstairs, unless it's simply coming through the floor? It really does smell like a corpse, it aint nice!