geraldthehamster gurgled happily, sounding much
like they were saying:

On Dec 19, 2:32Â*pm, 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 "opens onto the top of a drainpipe " I assume you mean an
underground pipe that leads to the sewer?

Yup. Just - I think - "grey" water.

In which case, is there a manhole downstream, from which you can rod
back up towards the house?

Yes, there is. I've just been to get some manhole keys...

....and promptly wished I hadn't...

It's not grey water. Definitely not. And it's about three inches below
ground level, and it's Really Not Very Nice In There.

The water board have been phoned.

I feel vaguely unwell.