Inspection chamber in the way of new extension

[dwtowner]

I want to build an extension to infill a corner of my house but there is an inspection chamber in the way. I'd like some advice on what I might have to do to fix this, please.

 

My house is laid out as shown in the first diagram. Yellow for the house, green lines for drain runs (with arrows for direction), and green circles for the inspection covers. IC 1 is the last chamber before it goes off to the mains. IC2/3 take the soil pipes from the house, and the gutters. IC4 provides a rodable change of direction. The pipe between 4 and 1 is approx 9m and is a single run through the foundations.

 

I want to infill the red dotted area (approx 1m wide) , which will be directly over IC4. I don't want to have to leave an access hatch through the floor of the extension to maintain access to an IC in that position.

 

I think that I will have to move IC4 so that it falls outside the red dotted area. Putting it directly in line with the existing long run would put it too far away, but if I put a shallow (<30deg) bend in I could keep it reasonably close to the existing IC. I've drawn this in the second diagram in purple. Is that right? Are there any alternatives?

 

Thanks.