For the record: Here’s my favorite realworld hack I got once told by my lovley coworker Roel:

How to clean a messy whiteboard.

Remember the situation when one used the wrong pen for the whiteboard and can’t clean it? Just take another pen which can be erased and go over the non erasable parts - suddenly everything gets clean away:

Or in the words of TvLesson:
Take another dry erase marker (preferably darker than the marks that you are trying to remove) and draw on top of the messy marks. Then wipe the marks away with a dry erase eraser or soft cloth.

The new layer of dry erase marker will lift and loosen the underlying marks. It’s simple but may not work for tougher messy marks.

http://www.tvlesson.com/article/13405_how-to-erase-a-messy-whiteboard.html