Answer: 50 Minutes = 309 gal
Step-by-step explanation: Every 10 minutes the amount of water goes up by 18, so after 50 minutes the water would be equivalent to 309 gallons.
Since the outside is 1.5 to 1, we take half of the value of the inside diameter and add it to itself to get the smallest value needed. 0.5+0.25=0.75
So the smallest diameter possible would be 0.75 inches.