P-Trap vs S-Trap Toilets — Wall Outlet or Floor Outlet

How to tell which one a building needs

Look at where the existing soil pipe goes. If the waste connection comes up out of the floor slab, the building needs an S-trap pan, whose outlet points straight down. If the connection comes out of the wall behind the pan, it needs a P-trap, whose outlet points horizontally backward.

On a new build, the decision is made by whoever designs the drainage, usually long before the sanitary ware is ordered. On a refurbishment it is already fixed in concrete and there is nothing to decide — measure it and order to match.

The names describe the shape of the trap in section: the S-trap curves down and round like the letter, the P-trap curves round and out. Both hold a water seal that stops drain odour entering the room; they differ only in which direction they release it.

Compared

Getting the order right

• Measure before you order, not after — Rough-in for S-trap, outlet height for P-trap. One site visit prevents a container of unusable pans.
• Do not mix within a project — Unless the drainage genuinely varies floor to floor, a single trap type across a development avoids sorting errors on site.
• Check what your market expects — S-trap dominates India and most African markets; P-trap dominates Europe, the Gulf and anywhere wall-hung is common.
• Adaptors are a last resort — Converter pieces exist but add height, add joints that can leak, and push the pan away from the wall. They rescue a mistake; they are not a plan.
• Wall-hung means P-trap — A concealed-cistern wall-hung pan has nowhere to send waste but backwards into the frame.
• State it on the purchase order — Trap type belongs on the PO next to the model number, not assumed from the catalogue default.

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