How to fix a leaking bathroom waste?

MegaEngine

I’m after some advice. I have a leak from upstairs waste pipe behind kitchen wall/kitchen oven. The house was built in 1998 so I assume it is plastic pipe work. The wall is damp and the leak has clearly been there for a long time, longer than I have been in the property. There is no access panel.

I have drilled and chipped some soft brick away and found (I think) 2 rusted old pipes, but dry (pic above).

Most water/dampness is on the left hand si de.
Should there be plastic waste pipe for this age (concrete slab downstairs and upstairs)? How do I keep looking for plastic waste pipes? I hope it is the access pipe seal/cap that needs replacing.
I was thinking remove the plaster, add a lintel for future access and remove some brick?

EricL

Hello @MegaEngine 

Welcome to the Bunnings Workshop community. It's sensational to have you join us and thanks for sharing your question about your leaking bathroom waste.

In this particular instance I suggest engaging the services of a leak detection specialist. They will have the equipment to pinpoint where the leak is coming from. Once the location of the leak has been determined, you can then decide how you would like to repair the leak. Further exploration into your wall cavity might not yield any results. 

It's difficult to tell if galvanized pipe or PVC was used in your plumbing. Using a sealer is only a temporary measure as the leaking water will find another way through your wall, it must be fixed at the source.  

If you need further assistance, please let us know.

Eric