Sounds like you have the basic distillation right but what are you using for a PSK tin? I think that an Altoids or tobacco tin sized container would be too small, the water would boil off so quickly that you'd constantly be recharging it. You might do better to pack along some foil to fabricate a boiler or pack a second mess tin or a canteen cup. Why are you distilling instead of just boiling? I don't see the need unless you're dealing with brackish or salt water. All of this pre-supposes that you have water to boil and fuel to boil it. Why aren't you just sticking with iodine or chlorine tabs? Are you just wanting a backup method of purification?

Ed