On Tue, 22 Nov 2005 09:18:29 +0000 someone who may be Chris Bacon
wrote this:-

Connections should not be made to the
stack within 200mm of the centre point of a lavatory connection.
This is to avoid the possibility of the lavatory discharge blocking
or obstructing smaller waste pipes.

If the connection is made opposite the lavatory one, 200mm below,
that seems to be in the perfect position for being blocked!

After falling for over 100mm the lavatory discharge is presumably
going vertically and thus unlikely to block a smaller branch. If the
smaller pipe is connected closer than 200mm then I imagine there is
still a horizontal component to its motion and so it may block the
smaller branch.

Having thought about it a bit more I suspect that the 200mm above
recommendation is to avoid siphoning water out of the trap in the
smaller waste.

That said it doesn't seem to happen IME.

That demonstrates that those who cam up with the recommendation were
right:-)


--
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