1 Gallon glass jug, about a gallon of 1.040 starter wort, foil covering the opening, and a stirplate is how I do it. I usually let it ferment out and then cool to the pitching temp after the beer is clear from the yeast dropping out. one or two days later I decant most of the beer, swirl the yeast into a slurry and dump it into 5 gallons of wort.
Works great every time! if it sits for more than a week before being used, (after fermenting out) I add some start wort again to revitalize the yeast the morning of the brewday. If I store it more than 4 weeks, it gets another gallon of start wort and I treat it like a vial... sometimes I even rinse the yeast to get rid of the dead ones.
Enjoy your lager experiance! It takes patience, but they are awsome!