Drainage advice

[Tjdservices]

Hi, a developer I'm working for has had some contractors install some drainage. I've told him I'm not happy with it but I don't know enough about it to advise him 100%. There are 2
flats, one first floor 1 ground. They have bought the kitchen waste from the 1st floor down in 40mm which the downstairs kitchen sink connects into and then it goes to a 4 inch stub stack. I have told him in my opinion that all the pipe needs to be 4 inch with the sinks being bossed in from 40mm on there respective floors. I want to get him to change it and have told him i wouldn't be happy to just pretend I haven't seen it so my question is as there is no WC running into it can I advise him to upgrade the pipe to 2" or 3" as he doesn't want to lose the space 4" would take up. Cheers

 

[Meady]

2" will be fine.

 

[JCSPLUMBING]

At least 2 inch with an AAV would be my advice if no WC connected. All depends on horizontal runs really. If it's mostly vertical, should be no problem

 

[Tjdservices]

Thanks, I've re run in 2" and fitted an Aav and rodding point