Gness, the rule for as long as I can remember, is for soakaways to be sited at least 4.5m from the building. I guess it's a fairly recent house. The usual thing was to get the digger to excavate a big hole, then fill it with stone, bits of brick etc.
The fact that the area rises, just means that the hole had to be dug even deeper to allow the inlet pipe to fall to the soakaway.
Nowadays, concrete chambers with an inspection cover on top are often used instead.
One possibility is to use an hydraulic "mole".......... the kind of thing used to "tunnel" a new gas supply to a house without having to dig anything up. Otherwise, there would have to be some excavation to find where the pipe run enters the soakaway.