Technical Booklet N Drainage·Page 12·Table 2.3
Minimum trap sizes and seal depths
Table specifying the required trap diameters and water seal depths for different appliances, with a note that seal depth may be reduced to 40 mm for ground floor appliances discharging into an external gully.
Appliances: Washbasin, Bidet - Diameter of trap (mm): 32, Depth of seal (mm): 75(1); Sink, Bath, Shower, Food waste disposal unit, Urinal bowl - Diameter of trap (mm): 40, Depth of seal (mm): 75(1); WC - Diameter of trap (mm): 75, Depth of seal (mm): 50; Sanitary towel macerator - Diameter of trap (mm): 40, Depth of seal (mm): 75; Food waste disposal unit (industrial type) - Diameter of trap (mm): 50, Depth of seal (mm): 75; Urinal (1-6 persons units) - Diameter of trap (mm): 65, Depth of seal (mm): 50. Note: (1) May be reduced to 40 mm for a washbasin, sink, bath or shower located on the ground floor and discharging into an external gully.
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