how do i connect a hose to the return line then to a bucket to find out how much water is coming out?

would it be safe to assume that the water draining from the tank is the same as the water being put into the tank?

i was using a head loss calc and it figures about 611 gph, and thats if i have 3 elbows, 4 feet of tubing that thats horizontal and 4 feet upwards