Tim Lamb wrote:

Can you get away with 110% of the largest container?

Yes there is some sort of derogation for capacity with multiple containers
but it just so happens that the layout of 3 1m cubes and 8 drums plus
enough distance to hold a jug under them means 110% + is available.

Latest advice is that resin sealer for block paving in addition to a
waterproof render is sufficient to achieve the required permeability.

AJH