Where is the underground drain?

[bengasman]

Got a client in first floor flat in south east London, ex council, with outside waste blockage, bit smelly and some water coming up outside.

No plans whatsoever, no sigh of manhole in their garden, Thames water have been and have no idea, council does not even understand the question: “do you know where the pipes are?”

Any clever ideas about finding out where the nearest manhole downstream is?
Don’t be shy, any input welcome, this one is a real biatch.

 

[twgas]

obvious but do any neighbours know

 

[TicklyT]

Are there any neighbouring properties built to the same design?
Do they have any apparent manhole covers that might give a clue where to start looking for your missing manhole?

 

[bengasman]

Alas, neighbours don’t know where manhole is either. The one next to that on either side are different.