[poisonblowfish]

Emergency, please help! My kitchen sink is blocking-up and I CAN NOT understand where all the water is draining!

I've tried;
Drain unblocker, then taking out the u-bend pipe under the sink (clean), then I checked the pipe at the back of the washing machine (as I could hear the water glugging from behind when the water slowly drained out of the sink). That pipe was clean. Then I tried poling from the manhole in the back garden. Some black gunge came out at first and it glugged, then nothing. Pipe from the manhole is now clear, so I am now at a loss as no water is coming out!

To note, there is a conservatory between the kitchen and the manhole. When I put the poles up the manhole as far as possible, it got all the way to the wall that joins the conservatory to the kitchen, and then it started hitting something hard. The poles came out clean, apart from the very tip which was covered in a sandy coloured substance which didn't smell.