Adrian wrote:
Outside the back of the kitchen, there's a deepish gulley into which
various drains empty.

It's about a foot deep right now. Soddit.

The bottom of the gulley opens onto the top of a drainpipe - which
clearly isn't flowing anything like properly.

I've borrowed some drain rods off a neighbour, but just can't get 'em
into the drain. I can't reach down enough to guide it manually.

Any thoughts?

When you say gulley, do you mean a trap? - is there water in it all the
time? - if so, you can't rod it, you need to get your arm in there and lift
out the offending blockage, which could be anything, so wear gloves.

A tip: pour a kettle of boiling water down there before you insert your
hand, don't worry, the water will be only warm by the time it mixes with the
ice cold stuff already there.
If you can't reach the bend at the bottom of the trap, you'll need a wire
coathanger, or similar, once its running free, put a dose of caustic soda
down there, preferably before you go to bed then it's got all night to do
it's magic without being diluted

--
Phil L
RSRL Tipster Of The Year 2008