Cleaning the landing boards?

[Bee J]

My girls are wonderful, but, after several years, the landing boards are covered with bee grime.  Some of it is sticky.
I'm curious if anyone can tell me how to clean the boards (which are painted) and not harm the bees. Plain water?  Soap?
 I thought I would do it after they've gone into winter cluster mode.   I also was curious if it would be simpler to just apply a
fresh coat of paint.   Any help anyone can give would be appreciated! 

[slaphead]

Warm water and a paint scraper work for me   

SH

[Bee J]

Thanks, SH!