hi there
a great scene from 'only fools and horses'
but no seriously.
if they need to be cleaned properly, then it is a case of taking them down, hang them on a frame and do it at ground level, even off site.
mild soapy water, and polishing clothes.
re access to take them down, if high up, then a mast lift, or tower, depends how many you have got to do.
any questions please ask
regards
martin