They have them at Home Depot and other places that sell plumbing supplies. Basically, they're o-ring plumbing fittings that regular OD plastic pipe, pex and copper tubing slips into and is then held with a water-tight seal. They cost like hell, so I figured the only good use for them would be in mating pex to standard copper. However, I was doing some domestic water system plumbing on the 4th of July and got into one of those situations where you can't solder the last joint because you can't stop the water from dripping into the fitting. After cutting and re-soldering a lousy 1/2-inch coupling about three times, I finally put a bucket under the leak and gave up for the night. At some point, it occurred to me to give one of them new-fangled Sharkbite thingies a try. Sure, a half-inch coupling was $5, but it worked like a charm. Since they can be disassembled with a special tool, it's like having a union in the water line without having to do any soldering. So even though I think they're priced way too high (what plumbing parts aren't these days?), I'm recommending 'em.