New soil stack in to existing man hole

I'm putting in a new bathroom and therefore new soil stack. There is a manhole 2.2m from where the stack will go, on a sloping driveway. The base of the manhole is 1m below the level of the stack. I've had building regs out who gave me some guidance, but just wanted to run my thoughs past those on here....

I'm thinking take the soil stack underground at the base by about 40cm then in to a rest bend. Gain sufficient drop from the 2.2m the pipe needs to travel to enter the manhole at the top of the benching & cut off here. Thing is, the pipe will enter at an angle. Is it ok to cut it off straight or should I fit an additional bend so it goes in straight? The discharge will be directly above the existing flow, but how much of a drop should I allow?

Thanks for your help!

I would expect the BCO to say that you need to either:

a) replace the chamber with one that has one more entrance point;
or
b) tee in your existing underground soil pipe, somewhere else, and add a chamber at that point.

I can't think of any reason not to do one of the above.

What guidance did your BCO give?

And what is he/she prepared to accept?

It's a concrete chamber deep in the driveway and shared with other houses, although I not too sure which. Therefore either of these would be a bit of a nightmare. BCO said I could drop a new pipe in to the chamber and as long as the exit point was low in the chamber and in the direction of the current flow this would be ok. This just seemed easier to me.

The thing that the BCO has apparently advised you to do seems quite a sensible, safe and pragmatic solution.

What's your motivation to do something different?

I do intend to do exactly as the BCO said, just a couple of bits I'm not too sure on.

Where the stack joins the underground system must I join in to a rest bend, or could I continue the drop a further 0.5m before angling off with a rest bend?

Also where do you get a branch that allows the WC discharge to enter the stack from the rear? All the ones in Screwfix etc. seem to require a side entry as there wouldn't be sufficient clearance from the wall for it to go straight in to the stack, but I've seen this done on other houses.

Thanks!