In an earlier contribution to this discussion,
Lobster wrote:


Mine goes out through the wall, and into a gulley - so the gulley
acts as a trap and there's no need for one inside.

But that implies if your kitchen sink empties into a gulley, then
similarly you wouldn't need a trap under the sink. Surely not so??


Strictly speaking, you probably wouldn't need a trap - but it would be
unusual not to have one.
--
Cheers,
Set Square
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