smelly toilet bowl even after replacement!

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.

Cheers from Aus
Henno

How is the bowl sealed to the flange? In the USA, the majority of toilets use a wax ring to provide the seal. If the toilet can rock in the least, it will break that seal since the wax won't rebound once it is compressed. Shims may be necessary. THen, in most places in the USA, require the toilet/floor joint to be caulked. This does a couple of things: it helps keep the toilet in place, and, it prevents near misses, dirty mop water, etc., to seep underneath the rim. Just not sure how things are typically done down under there...(hope to visit one day!).

Have you ever had your septic tank inspected and cleaned? One of two things could be happening, the pitch of the waste line is not sloped enough and effluent is laying in the pipe. The waste line has too much water sitting in it when most of it should be "dry". You septic drain field could be overdue for a replacement and the waste water is not draining and the tank remains full but may be draining just enough that water is not backing up into bath tub or shower. If you know how, you can remove the cover and looking inside the tank and you may be able to see the waste line from the home. Have someone flush the toilet and see how much water really dumps into the tank or maybe the sludge level in the tank has reached the waste line so it is time to get the tank pumped out.

In North America the product is called RID-X. <http://www.rid-x.com/how-do-septic-systems-work.shtml> Go to this page and it clearly explains how the septic tank works.