On Sun, 16 Nov 2008 13:30:14 GMT BigWallop wrote :
It's easier to dig down and build a brickwork chamber with a
lid. Make the chamber suit the lid you buy. A good lid is 3
foot X 2 Foot for a rodding access chamber, making the longest
face toward the direction of rod pull.

For the depth quoted by the OP (750-900mm), 600x450/24x18 would
be more usual. But yes, get the cover and frame first and build
the chamber to suit.

--
Tony Bryer, 'Software to build on' from Greentram
www.superbeam.co.uk www.superbeam.com www.greentram.com