A standard bottle trap is the reason most vanity drawers stop four centimetres short of closed. Drawer units and traps are bought together, not one after the other.
What a drawer unit has to accommodate
The waste pipe coming down from the basin, the trap, and the two supply pipes with their valves. All of it sits exactly where the back of a drawer wants to be.
The two solutions
A cut-out in the back of the drawer, moulded or sawn, that the pipework passes through. Makers who provide one publish its size and position; makers who do not leave you with a jigsaw and a guess.
A U-shaped drawer, moulded around the pipework from the start. It loses volume and gains certainty.
And the third, which is the plumbing one
A space-saving trap — flattened, hugging the wall — instead of a bottle trap. It costs a few euros more and it is the difference between a drawer that closes and one that does not. It buys that space partly out of the water seal depth, so read the figure.
What to check before ordering
Whether the maker publishes a cut-out, and what trap the unit is designed around.
Questions people actually ask
Is a door unit easier than drawers?
Considerably. A door unit swallows any trap without complaint, because nothing has to slide past it. Drawers use the space better and cost more in planning.
Can I cut the back of a drawer myself?
On a melamine-faced board, yes, and the cut edge has to be sealed — that is exactly where water swells chipboard. A unit sold with a moulded cut-out has already dealt with it.
Last reviewed 5 September 2026