I have a house on a concrete slab with two toilets plumbed (I think) to the same pipe under the slab. When we bought the house one toilet always had a black stain on the bottom of it and if left unflushed it would develop a terrible smell like a public toilet. None of the local country plumbers could explain it so eventually I bought another bowl. It is slowly developing the same scum on the bottom, no matter how much we clean it and will smell bad if left unflushed for a day.
I am in a rural area and connected to an Earthsafe septic treatment plant so have been told I can’t use chemicals that are too harsh as they will kill all the good bugs in the primary tank.
Has anybody ever heard of this?
Cheers guys and gals
Henno in Aus