We have all seen these things and most of us have probably used them. For me they are a necessity in that I need them for my mid sized Buddy heater, my Weber Go Anywhere gas grill and for the igniter burner on my Weber Performer charcoal grill. But they are becoming bloody expensive! They often come in packs of two and yesterday I saw them at Walmart for about $6.64 a pack. I saw them sold as singles in another store for $4.48 apiece. (It pays to shop!) Looking at the numbers-a 20# propane tank is supposed to hold 4.7 gallons or about 600 ounces. A one pound green bottle holds about 16.2 ounces. Dividing 16.2 into 600 goes about 37 times so theoretically you should get the equivalent of 37 small green bottles out of a standard 5 gallon propane tank. 37 times $3.32 is around $120-see the problem? Filling a 5 gallon tank is currently somewhere between $15-$20 so to buy the same amount of fuel in small green bottles would cost about another $100. That bothered me so I ordered up a fitting to fill the little bottles from the big one-about 10 bucks. I had saved up about a dozen of the little bottles and tried refilling them. The procedure is to place the big bottle top down-I set it on a couple of sawhorses-screw the little bottle into the fitting and turn on the valve. Filling takes but a few seconds and you can tell by the sound when the gas stops flowing. A new bottle weighs right at 30 ounces on my scale and I am refilling them to about 27.5 ounces or about 92% full. For pennies on the dollar. Okay, there are a lot of numbers on this post but the bottom line is that you can refill those bottles for a fraction of what you will pay for new ones. To get the best fill the big tank should be warm and full and the little ones cold. Right now I am just putting the little guys in a snowbank and leaving the big tank indoors overnight. Later in the season I'll use the freezer to chill the little bottles and just ambient temp for the big one. Remember to save your black caps.