Hi, Lowell. Why are you washing what you will be sanding away? I am not comfortable with the idea of putting any water on wood and particularly on soft, porous pine. Any dirt that is on the surface will be long gone (or turned into dust) when you hit it with the 36 grit sandpaper.
For what it's worth, I suggest that you try to get a copy of the November, 1999 issue of Family Handyman magazine. It has a great, long article about refinishing floors. Call 715-247-5060 during Central Time business hours to check availability. The cost will be $4 if they have it.