Fat Berg in the Communal Drain system.....

moneyistooshorttomention

Good chance you do have two stacks imo - as I've been told on my house that it shouldnt have just the one pipe draining off the bathroom and kitchen. That these days there would be two different "drains" so to say.

Mind you - considering some of what I've been told is correct here and manifestly turned out not to be - I'd check in your position.

pinklady21

The block is just about 50 years old, build early 70's, so fairly "modern". But that said, I have no idea what the building regs were then for drainage in flats. I imagine that the Council would have built them to standards of the time, so am hopeful that they can supply a detailed enough plan of the internal pipework.
If nothing else, it might help point to where the problem might be.....with luck there is not a serious structural problem with the route of the pipework - after all this time, I would be hopeful any such issues would have made themselves apparent and been fixed.