Air, water and performance tests for drainage, access provision for rodding, and how to read seal loss and odour symptoms.
Testing above ground
With every trap charged and the open ends plugged, sanitary pipework should hold 38 mm water gauge for at least 3 minutes while every trap keeps at least 25 mm of seal. A compatible soap solution can locate leaking joints under the prescribed air-test conditions; smoke testing is not recommended for PVC-U. Performance tests separately check seal retention during discharge. Fill a basin to its overflow level and release the plug, or flush a WC, then measure the seal remaining. Recharge the trap before every repeat. Carry out at least three runs and judge the largest loss; every run must retain at least 25 mm. For a range, the upstream appliances usually give the worst induced siphonage.
Testing below ground
After laying and backfilling, drains up to 300 mm are tested by air or water. For an air test, pump to 110 mm water gauge and let it settle for about 5 minutes. Then start from 100 mm: no more than 25 mm may be lost in 7 minutes. For a water test, allow up to 5 m of head at the lowest invert and at least 1 m at the highest. Allow the required conditioning period, usually one hour, then keep the specified test head by topping up over 30 minutes. The measured top-up limit is 0.15 litres per m² of internal surface for pipelines alone, 0.20 for a pipeline including manholes, and 0.40 for manholes or inspection chambers tested alone. For a circular pipe, internal area = π × internal diameter × tested length, using metres. Multiply the area by the applicable allowance; do not confuse it with the pipe’s cross-sectional area. The allowance is not permission for a known leak: investigate any defect you find. Where foul and surface water systems are separate, prove each connection reaches the right one.
Access for clearing blockages
Traps are removable or have a cleaning eye, and stack rodding points sit above the appliances’ spillover level. Before opening blocked pipework, assess retained wastewater and control its release. Water can be held above even a high access point. Below ground, provide access at the head of each run, at bends and changes of gradient or pipe size, and at junctions that cannot be rodded otherwise. From the start of a drain the maximum distances are 12 m to an access fitting, 22 m to an inspection chamber and 45 m to a manhole. For a chamber inside a building, the cover should be mechanically fixed and airtight unless the drain through the chamber has its own watertight access covers. Keep maintenance access available.
Further along a run the spacing can be wider. A shallow inspection chamber may be up to 45 m from the next inspection chamber or manhole, and deep manholes may be up to 90 m apart.
Reading the symptoms
Bubbling or outward seal displacement during upper-floor discharge points to positive pressure near the stack base. Check branch position, blockage and ventilation. A seal drawn down with gurgling suggests siphonage. If seals remain intact, leaking joints or covers are possible sources of drain air. These signs tell you where to look; none of them gives the whole fault. At handover, explain any anti-flooding valve notice, periodic checks of air admittance valves and the descaling routine for a macerator.