In addition to all the above (great) advice, when I first kegged, I kept losing co2 rapidly, like once a week. When I brought in the tank to my local gas supply place to either get it refilled or to see if the tank itself had problems, he gave me an o-ring to connect between the co2 tank and the regulator. The regulator nipple already has that permanent o-ring but even still it doesn't always seal since it lays flat. After that I had no issues going on over 2 years! I keep a bunch and even keep one taped to the regulator itself just in case.