However, getting filler wet with wax and grease remover isn't a good idea. That filler can soak up a bunch of it, do a test. Put some wax and grease remover over a panel with a spot of filler and look at it. Let it set a bit and the filler won't remain "wet" with the wax and grease remover on the surrounding metal will. It didn't evaporate off the filler, the filler absorbed it, that is not a good thing
I don't like the idea and personally never use it like that. No offense to you swvalon, it's just how I see it. There is nothing that causes paint product problems more than trapped solvents. Trapped solvents kicks every other cause in the butt when it comes to out and out causes for failure. So I treat solvents very seriously and letting the filler soak a little up, if only a little, is not something I am going to do. That is an old "trick" that has been going on for ever and many people do it, I just don't see a need in it.
Wax and grease remover should be wiped on wet and wiped off quickly to remove contaminates as they are suspended up in the wax and grease remover, that is how it is used.
I feel that if you can see a flaw, you can feel it. If after you block it and it feels good, apply primer, NOW you can see if there is a high or low. You don't want to do this every time, it isn't like you want to have layers of primer and filler like an autobody lasagna.
But the point is if you do your filler work until it feels good and apply primer, you WILL learn more and more as you go as to how to feel properly so you don't make the mistake of priming before it's ready. When you prime it, guide coat and block and when there are highs and lows that the primer can't take care of, feel it, learn to feel what these flaws feel like so next time you will feel them in the filler BEFORE you apply the primer so you can correct it before the primer is applied.