On Sat, 12 May 2007 07:27:46 GMT someone who may be
wrote this:-

Also I read that you should only use a shallow trap where it drains
into a hopper; not a soil pipe. I never knew this. Why is this? I
presume it is to prevent it siphoning?

Correct.

Shallow seal traps are liable to allow odours back into the
building.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54