A gulley in its widest sense is channel carrying water.
In residential properties a gully will usually be used for downpipe which collects water (e.g. rainwater) discharged from the downpipe and channels it into the underground drains. Gullies are also used for kitchen waste (e.g. waste water).
Gullies are prone to blockage from debris such as leaves falling into them, as well as water-borne debris such as food. If a gulley collects water from a sink then fat in the water will be deposited in the gulley which can build up and cause a blockage.
Gullies usually incorporate a grating to prevent larger debris getting into the drainage system. Such gratings need to be removed and cleaned from time to time. Any broken gratings should be replaced, as otherwise larger debris getting into the drains could cause a blockage which would be more difficult to remove.
There are a number of different arrangements for making the connection between downpipes and drains. If the water discharges into a combined drainage system the gulley should incorporate a trap (i.e. a U bend similar to that found in a WC) to prevent smells rising up from the sewers. This type of gulley is also recommended where the rainwater discharges into a surface water drain. A trapped gulley should always have water in the bottom (in the same way that there is water in the bottom of a toilet bowl.) If there is no water this might indicate that there is a crack at the base of the gulley, allowing water to drain into the ground near to the foundations where it could cause damage.
We carried out a CCTV drain survey which revealed the downpipe gully and pipework to be severely damaged. we replaced of the downpipe gully, pipework, connections and fully reinstated.