fit a 2 inch valve to the water butt 
Another way is the higher the water butt the faster the water will come out ,That if you have a hose fitted to it tap.
I.E the lower the hose exit is below the water the faster it will come out as the hose will act like a Syphon..

Another way is the higher the water butt the faster the water will come out ,That if you have a hose fitted to it tap.
I.E the lower the hose exit is below the water the faster it will come out as the hose will act like a Syphon..