I'm going to have to build a soakaway, which will take surface water from a
55m2 garden...there are no drains in the area.
The subsoil is mostly clay, but it's at the top of a hill - what size should
I dig the hole and what should I fill it with? - there are no limits to the
size of hole, nor to the infill material(s)

TIA

--
If God had intended us to drink beer, He would have given us stomachs.