I have a house built in the UK in 1906, which has an Interceptor Chamber. Having identified it as such, I need to figure out how to unblock it. Water is currently backing up all the way to ground level, very very slowly draining away.
I believe there is a flap to another pipe under the surface of the water, slightly below ground level which I should be opening and trying to unblock, but I'm not really clear what I should be doing. Reading online seems to indicate that it's the U-bend/trap that's blocked so I need to clear that. Mainly, I don't want to do anything that could just cause a blockage somewhere else.
What I remember seeing when it wasn't filled up with water was a 6 inch (diameter) pipe that went down as far as I could see (presumably until it hit the near horizontal waste pipe). Within that, taking up about half of the diameter of the pipe is a flat cap (also called a tea-pot lid I believe). Not really knowing what I was doing I tried plunging down the pipe as best I could with a normal plunger, but don't think it did much as it wouldn't fit properly because the tea pot lid took up much of the room. What should I try next?
tl;dr: See title.