Foul waste and open gully

11 Mar 2023
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United Kingdom
Can the foul waste from a WC go on the same underground drain as an open gully? Basically the the gully would drain directly into the foul waste pipe? Hope the sketch below shows what I mean. Black is existing, blue is new.


I can't send the WC drains to the SVP because there isnt enough fall to have the WC rest bend followed by the SVP rest bend in series.
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You want the loo to go to an open gully? No unless you're french.
If you mean connected underground to the shared waste pipe then yes.
Yes, but need a bit more info. How does the Gully connect into the manhole? If on a level invert, (i.e. incoming pipe enters the chamber at the same level as the through channel or just above it(, then you should be ok, but if not, then the WC connection needs to be done to avoid waste splattering everywhere when it enters the chamber.
The WC waste won't discharge above the open gully (lol). The gully is above the waste pipe. This cross section sketch might help.

Edit: updated with better sketch.


Underneath the gully is a 90deg elbow (confirmed( which I propose to replace with a swept tee (blue in sketch). The top invert of the existing pipe isn't burried very deeply, maybe 20 cm to the top invert.

The gully has a water seal formed by the casing and the removable cap. If I was to proceed with this plan, the 'poo pipe' wouldn't be exposed to outside due to the water seal, although cleaning the gully (lifting the cap) might be a bit unpleasant. Is this basically compliant?
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You don't need a rest/long radius bend - that is for use at the bottom of a single stack soil pipe - so that water doesn't "compress" at the bottom of the stack. You can google it for lots of pics.
You don't need a rest/long radius bend - that is for use at the bottom of a single stack soil pipe - so that water doesn't "compress" at the bottom of the stack. You can google it for lots of pics.
Good to know, although I don't even think I could get even a normal 90 in series with the existing soil stack elbow - not enough fall.
Picture of inside of the manhole may help.

Forgot to take one earlier, but have updated my sketch (see previous post). Does this help?
Sketch doesn't include Manhole, but by the sound of things, it should be OK.

As long as the Gully is trapped, it'll be fine. You may find yourself batter off by replacing the existing gully with a Bottle Gully, these have a horizontal outlet so may be easier to make a shallow connection, and means only one connection required to existing drain, everything upstream from there is new.
I have started taking things apart now and excavating. Unfortunately I will need to break up the concrete surround of both the gully and the inspection chamber, and temporarily remove them, to have enough room to line up the core drill for the wall. As this is, I may decide to relocate the gully slightly when re-installing it, and have it discharging into the drain from the vent stack (black diagonal line on first sketch).

The 'manhole' is just a shallow inspection chamber as shown below. The channels have a removable plastic cover moulded so that the channel and its cover have a circular cross section when installed.

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