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Separate drains or not to solve blockage issues

Postby DJH16 » Mon Aug 16, 2021 3:05 pm

I have an upstairs and downstairs wc discharging into a manhole. Black water then goes along a drain to another manhole to turn 90 degrees before going to the sewer. The drain between the manholes also collects grey water from 2 kitchen/ sink waste outlets. There is poor fall and a dip in the drain between manholes, causing frequent blockages.
It is clear the old salt glazed short section drain needs to be replaced. A drain contractor is suggesting some benefit would be gained by having the 2 kitchen waste grey water outlets not joining into the side of the black water drain, as simultaneous flushing of the wcs with running of the sink water can cause waste solids to become isolated in the middle of the drain. Instead, he proposes separate grey and black water drains, the flow only joining at the second manhole.
Any comments on this line of thought?
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Simply Build It

Postby stoneyboy » Tue Aug 17, 2021 9:25 pm

Hi djh16
It is difficult to understand why additional water flowing through a drain would cause stagnation of solids. Provided the junction between the soil pipe and kitchen waste pipe is installed correctly there should no be any reverse flow.
Regards S
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