Disconnecting Plastic sewage pipe

The professionals I payed to install a rain water storage tank failed to install a suitable anti-backflow valve resulting in the water tank filling up with sewage (when the drain was blocked). I have now dug down and found the plastic pipes which require the value fitting, have found a supplier of a suitable valve and don't know what to do next.

Can anyone tell me...
1. How do I disconnect the existing plastic pipes? Do they just pull apart and if so how much pipe am I going to have to expose to be able to do so? Is there a technique to do this easily?

2. I believe that I need an access to the valve but looking at the inspection chambers available they all appear to be for junctions. Is there a special type of inspection chamber for an inline valve or some other solution?

Thanks

Pipe size?

Layout?

Valve brand/model?

Photo?

Building Control notification?

Pipe size? 110mm

Layout? Straight pipe + some corners at one end which needs valve adding to. One end is attached to the main sewer at the man hole and the other end is attached to the overflow of the rain water tank. I had thought that I could unplug the straight piece from one of the corners cut it a bit shorter, add in the valve and that would be it. Depth of the valve will be about 400mm and needs access. I was hoping to buy one of the plastic access things but maybe there is a better/different way?

Valve brand/model?
http://www.metro-flowltd.co.uk/acatalog/drainage_fittings.html

Building Control notification?
Hadn't thought about this really. Seeing as they are the people who happily told me it was OK when it should have been obvious to them it wasn't I assumed they wouldn't care. I'll give them a ring though and check just to be safe. I guess in an ideal world they would take some responsibility.

dckidd said:

Building Control notification?

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Hadn't thought about this really.

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I see.

...I assumed they wouldn't care.

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Oh. Does this mean that you have thought about it?

I guess in an ideal world they would take some responsibility.

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You just lost my interest entirely. Let me know if/when you've accepted that the project is entirely your responsibility, as is doing it legally.

I fully accept my responsibility. Hence the "I'll phone them".

You'll have to forgive my cynicism as I have just paid a RIBA architect, a firm of specialist building project managers and structural engineers, a highly recommended builder and paid the council to do their bit but still ended up with 1500 litres of raw sewage in my rainwater tank and a whole list of other issues. And none of them accept any responsibility. I being left with having to pay for it and fix it am, to put it politely, a little annoyed. My kids who have the pleasure of flushing the toilets with sewage from the neighboring houses find it rather amusing, my wife, less so.

So if you are able to offer any more useful advice I would be grateful. If not then thanks for warning me about needing to contact the council. [/b]

I've no direct experience of your problem, but have scratched around a bit.

There's a useful looking document on this web site - if you select Anti-Flood Systems, then Anti Flood Sheets (1.4Mb), you can then download it and have a look.

Here's another site with an interesting drawing:
http://www.draintechnology.co.uk/pages/floodprevention.htm