Gurgling is the sound of air moving through water in your pipes. A drain that flows freely lets air move quietly. When something restricts the flow, air gets pushed or pulled through the water in the traps, and you hear it.
A single gurgle now and then is not always a problem. Regular gurgling, especially from more than one fitting, is usually an early warning.
Common causes
A partial blockage
This is the most common reason. Grease, wipes, hair or silt narrow the pipe, so water and air have to squeeze past. You may notice fittings draining a little slower than they used to.
A blockage in the underground drain
If the gurgle comes from a downstairs toilet or sink when you run the bath or washing machine, the restriction may be in the drain outside. Lift the nearest inspection chamber cover if it is safe to do so. If it is full of standing water, the blockage is further down.
Venting problems
Your drainage system needs air to flow properly. Most houses have a soil vent pipe running up the outside wall or through the roof, and many newer homes have air admittance valves (small grey caps on pipework, often in lofts or boxing). If a vent is blocked by leaves or birds’ nests, or a valve sticks, water rushing down the pipe can suck water out of the traps, causing gurgling and sometimes smells.
Trap siphonage
When a basin or bath empties quickly, it can pull water out of its own trap. You hear a gurgle as the last water leaves. This is more likely with long or small-diameter waste pipes.
What you can check yourself
- Is it one fitting or several? One fitting suggests a local issue with that waste. Several suggests the main drain or venting.
- Does it happen when another fitting is used? That points to a shared pipe or the underground drain.
- Are there smells? Gurgling with smells can mean traps are being emptied, letting sewer gas into the room.
- Are the inspection chambers flowing? Standing water means a blockage downstream.
When to get help
Call a drainage company if gurgling comes with slow drains in several fittings, water rising in a toilet or shower, smells that do not go away, or standing water in a chamber. Left alone, a partial blockage tends to become a full one at the worst moment.
Clearing the drain usually stops the gurgling. If it keeps returning, a CCTV drain survey shows whether there is a defect such as a dip or root ingress. See also why outside drains keep blocking.
For help in the Southampton area, see blocked drains or get in touch.