Lay your dollar bills flat on a piece of paper towel. Don't worry if they don't remain perfectly flat, the water will straighten the fibers.
Run the dollar bills briefly under warm water. Moisture on the surface enables soap absorption.
Apply a pea-sized drop of gentle hand soap to the tip of a soft-bristled toothbrush. Gently brush the surface of the dollar bills with the soapy toothbrush. Start in the middle of the bill and work your way outward, to avoid ripping the edges.
Flip the dollar bill over and repeat scrubbing on the other side.
Rinse both sides of the dollar bills under warm water and pat dry with clean paper towels.
Paper clip your damp bills to a taunt string as you would clothing on a laundry line.