Water Fill Concern - How To If No Pressure???

Yes, making a hole in the top of the tank will certainly cause some 'sawdust' to drop into the tank. My thought is that I'll have the tank full and after the hole is cut, add more water and let the floaters go out via the overflow pipe.

And after several different word searches, I found what I need on Amazon:
Valterra A01-2003BKVP Gravity Water Inlet

Thanks to all. And yes, this would be only used in difficult and unusual circumstances!
But I remember from a very long time ago: "Be Prepared"!!