The Sharkbite fittings (brand name for push-on fittings that's becoming a generic term, like Kleenex) and others using similar technology have an 0-ring that forms a watertight seal and a stainless toothed washer that supplies the mechanical retention.
Removal of the fittings is by means of depressing inward a ring at the "pipe" end of the fitting. This spreads the teeth of the toothed washer allowing it to be removed. Once properly installed, it will be nearly impossible to remove without pressing the release ring.
These fittings require that the outside of the pipe be absolutely clean and smooth. It is also absolutely essential that the pipe be FULLY inserted into the fitting -- it's easy to not get it all the way. Do not twist the fitting, as that would cause the toothed washer to scratch the pipe making it more difficult to get the O-ring to seal. If you ever hear of a failure of one of these joints, the most likely cause was that it was not fully inserted.
One caveat: if the fitting is allowed to repeatedly spin relative to the pipe, it could wear out the O-ring causing a failure.
If professionals don't use them, it's because the cost of the fittings runs as much as 10 times the cost of normal fittings.
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On a personal note, my cousin half-a-country away had a pipe in her house freeze and burst last winter. Since she couldn't afford to hire a plumber and had no plumbing skills, I advised her -- via facebook -- to use Sharkbite fittings. She successfully repaired her own plumbing with them.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.