Donot clean it at all...After all,isn't the point of having a 'fuge to provide algae a place to grow??? The more you have in there,the less likly it is to grow in the main tank...Also,the more algae in the 'fuge,the better it works at denitrafying the water.
Lastle,if you start disturbing the stuff(scraping) you will likly spread the spores into the main tank where it is less desiralbe....