Clay gully and trap question

[Andrew]

Hi,

My kitchen waste terminates outside into a clay gully. This has been sealed over with concrete.

This gully is a simple swept bend which connects to a clay p trap gully with a metal cover. When you look inside you can obviously see the trap straight down but there is also what I believe to be a rodding point just above it which is made out of old 3 inch internal diameter clay pipe.

This roddong point has no cover or bung or anything.

I want to remove the concrete from the gully (which I actually have done with success) and put a grate on there instead, but would need to bung the rodding point up to stop any smells coming back from the foul drain.

I have looked high and low and cannot find anything specifically for the job. The closest I've got to a solution is one of those expanding rubber pipe bungs used for pressure testing pipework. I'm just unsure of whether it's a good idea to have one of these permanently under the ground or not.

Any ideas?
Ta.