Backed up cubicles but not clogged?

[Brakerstrade]

Hi all and thankyou in advance for any advice you can give.
There is a three cubicle run of toilets upstairs in the building I'm renovating. When you flush one toilet, waste would come up in the bottom of the others in the run. We had a drain unblocking service carried out, hi pressure hose, cctv check etc. There is no blockage, so I can only assume its something else. If you flush food colouring in any of the three toilets, the water in the bottom of the other two changes colour to match. Any thoughts?

 

[ShaunCorbs]

Are they on the same level ?

 

[Chuck]

Any explanation that isn't a blockage will be unusual. Could be a combination of a downstream partial blockage and incorrect venting.

What are the venting arrangements? Does the system connect to a public sewar or a septic tank? Did the camera survey get to an inspection chamber? Have you checked the falls etc., comply with regulations?

Try lifting the lid of the first downstream inspection chamber and see how that affects the behaviour. Have you checked the falls and pipe diameters comply with regulations?

Has the system ever worked properly?

 

[Deleted member 120897]

It depends on where was surveyed with the cctv, manhole and sewer pipes only, then that will only show clear in those areas. Sounds like a blockage on the end of that pipe run/after the last wc, or the above suggestions.