Yesterday, I thought I'd take a look myself. It seemed to me that the drainpipe had slipped, and if I could move it up a centimetre or two, that would fix it. I could do that without getting out my non-insulated ladder.
I undid the screw that held the drainpipe onto a bracket, and a trickle of water came out. I could see that there was a 2cm thickness of crud at the bottom of the pipe, so I thought that if I could clear a hole in that, any water in the drainpipe could dribble out.
I got to work with the jemmy I'd brought to lever up the drainpipe, and was clearing the blockage when suddenly BAM!
Not only did it clear, but a whole column of water and stinking slimy black stuff EXPLODED out and SPLATTED everywhere, but mainly on me.
You can see where I was kneeling in this photo I took. The black line in the foreground with a clear patch either side of it was between my legs. Far, far worse was on my legs. My trousers have now been put in the "to go to the tip" pile. I don't know what the stuff was that coated me, but it wouldn't surprise me if I needed a course of antibiotics next week. There were entire peanut husks in there, partly dissolved by the sludge.
I could have cleared the resulting unhygienic mess a lot more easily with a hosepipe, but there's a hosepipe ban so I had to use a bucket. I probably wasted far more water this way than I would have done with a hosepipe, sloshing it on the filth to get it away, but it worked.
Only ... see that metal grid flush with the ground that leads up to the drain? That wasn't collecting any of the backwash from my sloshing. I took off the grille (handy tools, jemmies) and found it was choked up with crud of its own. I bailed it out, and discovered why: there was a blockage where the half-pipe under the grille reaches the drain outlet. The reason there was a blockage was that it didn't have a proper hole into the drain housing. It looked as if someone had hit the plastic of the drain cover a couple of times with a hammer and screwdriver, leaving two inadequate holes with a tooth between them for everything to catch on.
I managed to chisel out the tooth, but the hole is still quite small, I expect it won't be long before it blocks up again. Maybe it's meant to be small so effluent from the half-pipe doesn't block the drain itself, although nothing big gets in anyway because of the grille.
I hoisted up the drainpipe a little so it's probably better-connected at the top. I made a new hole to screw it to the bracket. The original screw was maybe 4cm long, and I hold it partly responsible for causing the vertical blockage. I replaced it with the shortest black screw I could find that would do the same job, although it was still 25mm so I don't expect it will be fault-free itself.
I then spent some time sloshing down more water, because I'm more afraid of my wife's complaints that I left a mess than I am of being accused by my neighbours of water wastage during a drought. As far as I'm concerned, it was a health-and-safety issue.
I'll see if the drainpipe is working properly again next time we have rain, which if this summer so far is anything to go by will probably be mid-September.