Connection to steep sloping lateral drain

[JackOrion]

We have a 100mm lateral drain that we will be connecting to. Runs right through our plot and is five metres or so from the edge of the house. This existing drain runs down a steep gradient (perhaps around 30 degrees), before it drops down to the mains below. We're in a valley hence the slope, and it's an old Victorian drain. We have been given the green light to connect by the water company for domestic foul water (with a soakaway for surface water).

 

Who governs the connection method and gradient of our connection? Building control or utility company?

 

Does anyone have any experience of connecting to a steep sloping lateral drain such as this, and is it likely to be a complex procedure? Have been reading quite a bit about maximum recommended gradients of 100mm drains being more like 14 degrees to avoid solids being left behind, and wondering whether the existing drain gradient makes our job trickier. We can control the gradient of our connection as we're on a plateau midway down the slope.

Edited 4 hours ago by JackOrion