Filling knot holes and flaws before finishing

Q: We are installing utility grade oak hardwood flooring. We like the look of the large knot holes and other flaws in the wood. My questions is how to fill these holes before finishing?

We are planning on finishing with a water based polyurethane (no Stain). I was wondering if there is a clear epoxy that I could use to fill the holes which could then be sanded with the rest of the floor before finishing. A builder told me to take the sawdust from sanding and use the polyurethane to form a paste to fill the holes prior to finishing. What would work the best?

A: There are water based fillers you could probably buy from the place you bought the flooring, if it is a hardwood flooring retailer. When dry, they sand off well and blend well with the floor colour. ********* is an example of such filler.