Drainage fixtures, blockage materials and symptoms
Drain blockage library
Guidance on common drain blockage materials, the fixtures they affect and the symptoms that can distinguish a local restriction from a problem further along the drainage system.
A slow sink on its own points somewhere different from several fixtures backing up. A gully that overflows only during rainfall raises a different question again. Looking at which outlets are affected, and when, helps narrow down where a restriction or fault may lie.
Affected outlets: one sink or toilet, several fixtures, or an outside drainage point.
Timing: continuous, after another fixture discharges, or only during rain.
Material: suspected wipes, grease, leaves or another known obstruction.
Current condition: slow drainage, backing-up, overflowing wastewater or loss of use.
Reference sources for this library
The references below cover the products, drainage systems and blockage materials used in this library. Manufacturer information describes the named product or system only; it does not establish the condition, suitability or requirements of a particular installation.
How soil stacks carry discharge from connected sanitary appliances, the symptoms of a shared restriction and the checks needed when several fixtures or floors are affected.
An air admittance valve ventilates discharge pipework; it is not itself a point through which wastewater flows. Noise or odour alone does not establish that the drainage is blocked.
Guide information
Whether there is actual slow drainage or backing-up as well as noise or odour.
Whether several fixtures on the same branch or stack are affected.
A bath connects to the waste system through a trap and waste pipe. Standing water may come from a local restriction or from a shared branch further along.
Guide information
Whether water stands only in the bath or other bathroom fixtures are also slow.
Whether drainage changes when a nearby basin or shower is used.
A bottle trap retains a water seal beneath a fixture. Slow drainage, leakage and loss of that seal can produce different symptoms and should not be treated as the same fault.
Guide information
Whether the main symptom is slow drainage, leakage or odour.
Whether nearby fixtures show similar drainage symptoms.
A dishwasher normally discharges into nearby waste pipework, often at the sink connection. A restriction may affect the appliance connection, the sink waste or a shared branch downstream.
Guide information
Whether water backs up at the sink or appliance during dishwasher discharge.
Whether the sink also drains slowly when the dishwasher is not running.
A shower outlet feeds connected waste pipework. If water backs up when another fixture is used, the restriction may lie in a shared branch rather than at the shower outlet.
Guide information
Whether the shower alone is slow or other bathroom fixtures are affected.
Whether water rises in the shower when a nearby fixture discharges.
A soil stack access fitting provides a point for inspection or maintenance. If wastewater is backed up behind it, opening the fitting can release sewage.
Guide information
Whether wastewater is backed up before the access fitting is opened.
Whether other fixtures connected to the same stack are also backing up.
A washbasin connects through a trap and local waste pipework. If nearby bathroom fixtures are also slow, the restriction may be beyond the basin connection.
Guide information
Whether the basin alone is affected or nearby bath or shower outlets are also slow.
Whether there is slow drainage, leakage or odour at the basin trap.
A washing machine pumps water into a waste connection that may share downstream drainage with other fixtures. A restriction can become apparent only while the machine is pumping out.
Guide information
Whether the problem appears during the washing machine pump-out cycle.
Whether a sink or other fixture sharing the drainage also backs up.
A waste pipe branch can receive discharge from more than one fixture. When several connected outlets are affected, the restriction may lie beyond an individual trap.
Guide information
Which fixtures appear to share the branch and which of them are affected.
Whether the symptoms change when another connected fixture discharges.
