An important data to know is the time and volume that a tank or container can drain liquids from the drainage valve using only the power of gravity.
Size - gallons per minute - Liter per minute
1" - 6 gpm - 22.7 lpm
1 1 /2 " - 13 gpm - 49.21 lpm
2" - 23 gpm - 87 lpm
2 1 /2 "- 35 gpm - 132.5 lmp
3" - 50 gpm - 189 lpm
4" - 91 gpm - 344.5 lpm
5" - 142 gpm - 537.5 lpm