The video is self explanatory but I'll explain. I believe in having super clean, tools that are in good shape for speading filler. Just because it is a "necessary evil" to use these tools to spread filler that will then be sanded doesn't mean that your tools should be held to any less standard than any other tool. Yes, they will be covered with filler and all goopy, so what, so is your paint gun all covered with paint, buy you clean it. If you don't clean it you will end up with a poor spraying gun, and it will be spitting crud from previous paint jobs on the one you are currently doing. What makes a spreader and mixing board any different?
The smoother you get the filler on, the less sanding needed, right? The nicer the tool the nicer the filler will be spread. The nicer the filler is spread, the less sandign needed. I don't know about you, but I am all about less work if I can help it.
So I treat my mixing board (at least right where the filler is mixed, the rest looks a little funky) like any other tool, I keep them clean, and with precise edges to mixing as well as spreading is easier.
The video shows how I keep the edges of the tools nice.
Brian