Fuel Return Ratio
The total engine fuel flow, on a 3GM30 ( 27hp ) is not much greater than the engine fuel consumption as the return flow is low.
On a 6CX-ETE ( 420hp ) the total flow is 846 litres per hour at full power. The return flow is 756 litres per hour give or take a bit.
So, you may wish to take my previous advice with a grain of salt, and do what you can to confirm the approximation.