Gallons, Friction loss, size question.....

[Aqua Man]

I am attempting to double up the circulation on my 375gallon tank. Now currently I am using a Dart which is rated at 4700gallon/hour with a 1 1/2" draw from the sump. I am thinking of T'ing that so I can run 2 x 4700gal/hr Darts. I am thinking that is possible as I am a pumper operator on a fire truck and we push an average of 1200kpa ranging from 50-250 GPM(gallons per minute)on our 1 1/2" attack lines; so I am assuming the 1 1/2" PVC pipe can handle 9400 gallons/hr? as drawing? the head pressure to the bulkhead on the draw is about 20". also now the back of the tank is drilled for 2 x 1" returns.... now can 1 x 1" return handle 4700 gallons/hr, as I will be running one Dart per return?

Thanks