Calculating pipe size for closed loop watering system

[Ice_ca]

I am building a closed loop watering system and need help determining the minimum size pipe I need for the return drain pipe. The system will pump water from a reservoir through spray nozzles into 4 containers at a rate of 300 gallons per hour. Each container will have a drain pipe in the bottom connecting to a central pipe which will feed the water back to the main reservoir via gravity with a drop of 4 inches.

My question is "What is the minimum size drain pipe I require to ensure that all the water is being returned to the reservoir?"

Any feedback would be appreciated.

 

[cipher42]

Is it pumping at 300 gallons/hour for each container, or is the 300 gallons/hour spread out into all four containers?

 

[Ice_ca]

Is it pumping at 300 gallons/hour for each container, or is the 300 gallons/hour spread out into all four containers?

Sorry, yes the 300 gal/hr is spread over the 4 containers.