Sanitary Piping Best Practices 1

The main elements of sanitary pipework  are:

  • Traps
  • Branch discharge pipes
  • Discharge Stacks


In the field of plumbing, pipework and drainage, a trap is a shaped pipe that retains water. The retained water acts as a seal to prevent foul air from escaping out of the system and into the building. The depth of the water in the seal and the diameter of the trap depend on which plumbing appliance the trap is connected to.

Trap specifications:

  • Washbasin or bidet: Trap diameter of 32 mm and water seal depth of 75 mm.
  • Bath or shower: Trap diameter of 40 mm and water seal depth of 50 mm.
  • Food waste disposal unit, urinal, sink, washing machine, dishwasher: Trap diameter of 40 mm and water seal depth of 75 mm.
  • WC pan outlets of below 80 mm: Trap diameter of 75 mm and water seal depth of 50 mm.
  • WC pan outlets of above 80 mm: Trap diameter of 100 mm and water seal depth of 50 mm.

Note: all of these specifications are the minimum sizes for the water seal to work.

Most traps are designed such that they can be removed from the pipework with relative ease. This allows the pipes to have a secondary use in trapping and removing objects that are inadvertently sent into the pipework or build up as sediment over time. In this way, potential pipework blockages become far easier to remove, pipes are easier to clean and valuable items such as jewelry can be reclaimed.

Types of trap:

The P type trap:

  • This trap has the U pipe shape of a basic water seal.
  • The U becomes a P in that the trap causes the flow to make a perpendicular change in direction, generally from moving vertically down to a horizontal direction.

The S type trap:

  • An extended version of the P type where the snaking structure continues past the seal allowing the flow direction to remain, vertically down.

Both the S and P types are relatively large, but are easy to dismantle and clean.

The Bottle trap:

  • This trap involves the follow through exit pipe branching above the water seal.

Other traps:

  • Shallow traps: This trap has low vertical depth and thus is often used where space prohibits a bottle or P/S type trap. The downside of this is that it will not comply with regulations. This means that a second trap with the correct depth will be required further down the plumbing network. A shallow trap can be useful as a preliminary to catch most objects however.
  • Twin bowl sink trap: typically consisting of a P type trap with a second waste inlet.

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