Draining Charged Pipes to a Rain Water Tank

How to calculate the size of Charged Pipes draining to a Rain Water tank. Further detail can be found here
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Charged pipes are necessary when an above ground tank is positioned away from the building, (or quite a distance from furtherest downpipe,) and the pipe must travel underground before rising again to discharge into the tank.
This means that water will always be trapped in this underground loop after the rainfall event. Hence the definition of being called "Charged".
Strangely there are no mention of such things in any plumbing code, as it is not strictly a stormwater pipe flowing under gravity, nor is it a water pipe flowing under pressure. so the powers that be started to ask some embarassing questions.
This Video attempts to shed some light on the subject by showing you how to design a pipe to the hydraulic grade line.