Often, the softener's installation manual will specify to increase the drain line diameter when the length is to exceed 15'. While 1/2" tubing can easily flow 2.2 GPM, a long drain length will increase flow resistance. While a small reduction to the flow rate is not usually critical for most water transfer applications, a specific flow rate is required for media backwash so any restriction can negatively impact the results unless compensation is performed.
The usual recommended backwash rate for softening resin is 4-5 GPM per ft2 to acheive 40%-50% bed expansion. For a 10" diameter tank, this calculates as 2.2 - 2.7 GPM but because you are using a Vortech tank, the DLFC rate will need to be reduced by 15-20% as Ditttohead stated in post #9. These flow rates are based on a backwash water temperature being 60 - 69F. If the water temperature is 50-59F, then the flow rate will need to be further reduced by 10% whereas if the water temp is 70-79F, the DLFC rate will need to be 10% higher.