Ken, Go to McDonalds or Buger King and appropriate a soda straw. Poke the vasoline/cotton down into a chunk of straw. Pinch with hemostat or needle nose pliers and use a match to melt the straw closed.
I've made tons of these containers, all sizes, and never had a leak. Actually, you can open the straw and extend out some cotton and light it like a candle wick (if you're using a match) or, with your hotspark just pull out a plug of cotton and spread it out a bit.