I have installed a 5" maple plank floor (rustic maple... streaks, knot holes of which some are missing, and mulitple colors) which came out nice. Looks great just plain. Back to the real world - it needs to be finished... I am sanding a filling knotholes at this point, some quite large (1-3"). I have heard of filling the holes with everything from Famo-wood to epoxy, sawdust mixed with glue... what to do? I am applying a stain sealer before the stain and poly. I would like to get the knotholes dark to where they don't stand out. What is the best product to purchase or fabricate to fill these large voids?

I would use epoxy to fill large rustic maple knot holes, If you fill a dark brown/black knot hole with wood filler it would look strange IMO.

Use a combonation of clear, and black epoxy, Clear for the holes/knots where you can see the not itself (it will conform to the color, and black in some spots like knots that are large enough to see the subfloor. Use the super fast drying stuff

I just did a rustic #2 oak floor and I filled knots and splits with Timbermate in Ebony color. It was pretty easy to work with and looks great!

Greg