WARNING: This is gross, I mean revolting disgusting horrible. Do not read if squeamish.
John was a wee bit alarmed to notice one of the manhole covers in our back garden lifting above the ground. Close inspection revealed that it was people effluent pushing the lid off (yuck!). A wonderfully moulded (to the bottom side of the cover) two foot across circle of sculpted... er, human muck. How solidified I couldn't say as we didn't want to interact too closely.
It wasn't actively overflowing, or made worse when we flushed the toilet upstream, but we still thought best to sort it quickly.
We went down stream as it were, the next drainage access point, only 12 feet away, was entirely clear, thankfully. Clear access to the 4-inch diameter clay pipe about two feet below the ground surface.
From the all-clear manhole, try to aim pressure washer upstream. Small amount of material appeared to flow out, but not much and no reduction to the emerging human poo sculpture. Luckily we were working on a straight section of not-too-long pipe, something with bends in it or with a blockage further along would have called for other solutions. There are special attachments you can buy for a pressure washer to clear the drains (look in likes of Machine Mart). Problem is that these can cost more than £50 and we'd have to wait a few days before trying one out.
A pressure washer pushes material back up the pipes, causing the scent of faeces to waft strongly out of our kitchen sink (puke).
Next day friend also offered to loan us her drainage rods; it's quite a generous offer when you think what would be involved! But again expensive option to buy our own, and tricky to use them properly because losing rods deep inside the drains is quite a common problem. We probably would have resorted to this if the section of pipe that needed clearing had been much longer.
We considered getting strong chemicals in but opinion seems mixed about whether they work and they are certainly nasty to the environment. I don't see how anything but physical cleaning was going to sort out our blockage in the end.
Get the regular hose and bind a stick to it, effectively, to break the mess up. Our "stick" was actually a bit of old aluminium extrusion, about seven feet long, bound tightly to the hose with an old bicycle inner tube. The extrusion is flexible, so can bend a fair bit with the hose but hard enough to excavate away. Tape wouldn't work to bind the extrusion to the hose (water would dissolve the glue). Turn hosepipe up to maximum flow, shove stick up pipe and poke around. Maybe don't poke too hard, don't want to damage the pipe itself.
This worked fairly well, plenty of material came down the drain. And a noticeable settling of the sculpted yuck pushing up the cover.
I have read of people using their wet-dry vacuum cleaners in a blockage problem like this; drawbacks of that approach are pretty obvious (would you ever use it for anything inside your house again?).
Time to stir the stinking mound and try to break it up from the top (opportunity for several horrible puns about sh!$ stirring, the c?&p home-owners have to deal with, etc.) We found an iron spike about 1 metre long and commenced poking and mixing. The mound finally collapsed (barf) and with a bit of hosing and more poking a rather clogged up drain was made all clear.
Pressure washing the sculpted muck from above would have been a disaster, fine spray of microparticles of human faeces would have ended up everywhere. We needed to expect that blockages down pipe were mostly clear so that the material could hopefully just fall down and drain away with physical prodding and a bit of gentle hosing.
You obviously need to have a rather strong stomach for this sort of thing. All implements washed with strong detergent afterwards. We don't blame anyone who calls the professionals instead!
Total Cost of clearing the drain: About 2 hours of our time and maybe £1.50 = The approximate cost of 500 litres of tap water. Not bad.