We have clean windows recently at Upper Church Street in Bath externally and internally.
All windows are sliding sash type windows with little squares and frames all around them. To clean them properly on the outside, we have used reach and wash system, including soft brushes and purified water. We gave it a good scrub twice or three times and finally rinse them off underneath top frames. On the inside we have cleaned them with soft soapy applicator, squeegee rubber blade and scrim to polish off any left marks and wipe frames off.
The clean really made a difference as the owners have a great view now to see outside.