An aqueous slurry containing particles with $S G=4$ and a range of sizes up to $300 \mu \mathrm{m}$ flows upward through a small tube into a larger vertical chamber with a diameter of $10 \mathrm{~cm}$. You want the liquid to carry all of the solids through the small tube, but you want only those particles with diameters less than $20 \mu \mathrm{m}$ to be carried out to the top of the larger chamber. What should the flow rate of the slurry be (in gpm) and what size should the smaller tube be?