First of all, what's it got in common with window cleaning apart from the use of water?
Secondly, have you read this?
3. Managing washings from wheeled waste containers
Wheeled waste container washings (wash and rinse water) may contain detergents, disinfectants
and waste residues which can all cause pollution. Don’t carry out washing in an area that drains to
surface water drains. You must discharge the washings to either:
a foul sewer at a specified location at your own premises, with the agreement and
permission of your local Sewerage Provider
or
an on-site sewage treatment system that’s
designed to deal with this waste and where the
system’s treated effluent discharge is covered
by an environmental permit from us.
from
http://www.environment-agency.gov.uk/static/documents/Business/wheeled_waste_bin_cleaning.pdfStill want to do it?
I'm with Chris P Bacon - you should be thinking of adding tree surgery while you're at it. After all, some of your customers surely want their trees lopped, don't they?
Vin