I get mine from USComp in the one gallon metal cans also. I, like Charles, tried to find the simplest solution... Mine cost about 2 pennies.
I don't even mess with the twist cap hole. Instead, i use a Phillips screwdriver, and knock a hole in the top at one corner. Then, at the opposite corner, i knock two holes. The single hole is where i pour from, and the double holes act as vents to let air in the can so there is no glugging. Then, I use two pieces of duck tape to cover the holes. When i want to pour, i remove the tape from the pouring side, and just pull it back far enough on the other side to expose the ventholes. I lose maybe 6 or 8 drops or so per gallon doing it this way, and all it cost is a couple pieces of duck tape!
P.S. If you use this method, it helps a bunch if you twist the can as you stop each pour. It cuts the flow of PR instantly, and you lose nothing usually. I can pour straight into those little 3 ounce dixie cups without worrying about spills, or accidental overflows.