What should be done to control the bead of colour collecting at the lower edge while making a flat wash?

Correct answer: Carry the bead forward at a steady pace

The governing principle of a flat wash is even distribution of diluted pigment. Keeping the bead, or small pool of colour, moving forward at a steady speed prevents one area from becoming darker and reduces streaks. Drying the brush removes needed moisture, turning the paper does not control the wash, and washing after each stroke would disturb the paper and colour.