John Guest has been making what seem to be very nice push-to-connect fittings in the UK for a long time. I’ve only used the US versions, and I’ve never seen one

John Guest has been making what seem to be very nice push-to-connect fittings in the UK for a long time. I’ve only used the US versions, and I’ve never seen one fail. If you avoid putting bending stress on them, they seem quite secure. John Guest also has some very nice “ProLock” build-your-own-manifold fittings. For what it’s worth, there are a couple of applications for which plastic or stainless steel are the only credible choices. Carbonated water is dangerous when in contact with copper or brass, and boiler condensate (which is basically carbonated water) will rapidly destroy copper or brass. So your boiler condensate drainage system generally ought to be made entirely of plastic. I’ve personally had some rather impressive failures of copper pipe due, I think, to aggressive water at excessive velocity. Copper’s ability to resist corrosion is finicky.