RCW 46.44.070: Drawbar requirements—Trailer whipping or weaving—Towing flag.

The drawbar or other connection between vehicles in combination shall be of sufficient strength to hold the weight of the towed vehicle on any grade where operated. No trailer shall whip, weave or oscillate or fail to follow substantially in the course of the towing vehicle. When a disabled vehicle is being towed by means of bar, chain, rope, cable or similar means and the distance between the towed vehicle and the towing vehicle exceeds fifteen feet there shall be fastened on such connection in approximately the center thereof a white flag or cloth not less than twelve inches square.