On Sun, 19 Jun 2005 09:00:55 +0100, a particular chimpanzee named
"Colin" randomly hit the keyboard and
produced:

Someone suggested that maybe possible to place a smaller diameter pipe
through the middle. Problem is, the run is well over 100m. I guess that it
would not be wise to go from 9 inch to 4 inch as it may cause things to back
up a bit(?)

Provided it's laid to a fall, it shouldn't do. You might want a
couple of chambers along the run; the max recommended length between
inspection chambers is 45m. As I said before, you could consider
lining the pipe.
--
Hugo Nebula
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just how far from the pack have you strayed?"