Mike Taylor wrote:
"There shouldn't be any "rocks" in your soakaway."
What should be in the soakaway then?

Normally, air.


In "normal" terms a soakaway is a hole in the ground filled with rubble
(Rocks if you want) into which the rainwater pipes go.

That's more of a french drain. If you fill your soakaway with stuff,
there's no holding space for water.


Sometimes nowadays a hole in the ground is lined with a perforated concrete
ring system, then capped and is hollow but this is not usual, certainly for
properties of more than a few years old

They used to be of brick.