Are you sure you have 1 gallon left? I've had my Berkey for several years and I only have several ounces left. The filtering flow rate does increase with water pressure.
Since it is a gravity feed system it isn't going to be a speed demon.
The first thing a man will do for his ideals is lie. --Joseph A. Schumpeter
A man is none the less a slave because he is allowed to choose a new master once in a term of years. --Lysander Spooner