Hi, I know the question above goes back some way, but I have the same trouble, a few bubbles in the pan after the flush. No blockage, I have poured several buckets of water down. The bubbles seem to produce a sewer gas smell. What I don't understand is it seems worse sometimes than others. I even began wondering if it depended on the wind direction. (I'm talking of the weather here!) Our WC is a conventional affair with a 4in soil pipe, the flat next door has a macerator and small bore pipe. The stack is 13 feet away. We had very bad smells from time to time, (like when the bloke next door ate something iffy - sorry! )then the landlord changed the pipework, before that next door's pipe joined our soil pipe as it went under his floor. This is probably Micky mouse plumbing at best! This was one flat made into two.

You have a partial blockage downstream from the toilet. Let me explain what's happening. The toilet flushes. This discharge races down the sewer and bangs into a partial clog and bounces back sending a bubble of sewer gas back up the line. The gas escaping from the -------- is what you smell. After bouncing back the water drains past the clog. To fix this problem the drain line downstream from the toilet must be snaked and cleared. Good luck, Tom