Correcting Sewage Connection

[mike2016]

I had a survey done a few years back and they misidentified the two drains at the rear of my self build property. This fed into the Architects drawings then used by the builder last year and I've only now discovered while trying to install rat flaps that I'm plumbed into the wrong one for sewerage. I've yet to lay the storm drains myself. 

 

I measured the distance and depths and have come up with the diagram below. I think I'm just about ok - currently the foul drain connects to the deeper storm drain and I just need to extend it to connect to the shallower foul drain. It's a sharp 90 degree bend then. Any advice / gotchas / am I ok / will this work? No experience with this so just checking my homework here! Thanks. 

[Russell griffiths]

You shouldn’t put a sharp 90 underground, either install an inspection chamber just before the connection, or a very slow long radius bend. 
 

how exactly are you connecting to the sewer, is it a saddle or are you cutting in and installing a junction. 
 

a few photos would help with this. 
 

and if the storm drain is deeper than the foul then your current pipe will be to low in the ground, you will need to go backwards up the run of pipe and re lay the pipe to the correct fall. 

[mike2016]

There are two shores on my land that are the highest point in the run for the row of houses. The builder last year knocked into these shores to connect up my drains. My house in feeding in from the bottom and the mains are off to the top of the pictures. I plan to dig out the existing pipe to correct the fall and extend from the storm drain to the foul drain. Was curious about the sharp bend, once I excavate I'll have a better picture and agree any sharp corners are to be avoided although the concrete rainwater harvesting tank limits the bend radius a bit but will work to improve it. Cheers