I have fitted 450mm inspection chamber (had to be changed from 300mm
after correspondence with BCO (grrrrr).
I know about bedding the drainage runs in pea gravel etc. But what
about the chambers themselves ? A couple of related questions.

1. The plastic chamber has a hollow base formed by the underside of
the moulding, and little legs around the edge. I've left a good space
8" or so underneath to put concrete to give it a good foundation. It
is currently supported where the concrete will be, by bricks. How far
do you usually put in the concrete - just supporting the little legs,
or right up under the moulding so the whole thing is supported
underneath ?

2. How do you backfill around the chamber ? With pea gravel, or with
soil. Note that eventually a recess cover filled with paving will be
placed on top, and this will need to be supported by a good ring of
concrete around the chamber, and I can't see how this concrete can be
supported on pea gravel around the chamber.

Thanks,
Simon.