Sanding Middle Floor Filler in Joint

[grubburg]

Any secret to getting this out? I already belt sanded. I was planning on using an edge sander, but am apprehensive about messing up the level. Does all wood filler need to be gone?

Pic.

 

[Mark Brown]

If your floor sander is not sanding out your filler, then your floor isn't flat. You need more sanding is all

 

[highup]

Belt sander or drum sander?