To determine the flow u hav to estimate liao. 2000l/hr after gg thru all the bends and height, prepare for approx 10% drop in flow. Tat leave u with 1800l/hr, using the valve at half turn will give you approx 900/hr. Turn 3/4 shd put u at approx what you need.
Unless u have precise measuring equipment like flow meter or use a 5L container and measure how long to fill then do the math> too tedious.