honey and sting

A lot of my friends have them. They are sold by a local sustainability organization. They are completely contained (no mesh necessary) and tap into your drainpipe with some kind of diversion tube. If the barrel fills, the rain gutter just acts normally, spewing water onto the ground or wherever it goes. To get water out of the barrel, there is a tap toward the bottom like in a large water jug. You attach a hose to that and you can water a garden or fill a fountain or whatever. These cost $75 with an additional $50 if you don't install it yourself but have the organization do it. (That price varies a lot as the organization adjusts how much they need to have as a fund-raiser)