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Generally, when draining one's plumbing system all the faucets (or at least the ones at the ends of the manifolds or loop) should be opened so that all the water drains from the system and as the water drains, the space left behind is filled with air. If you neglect to do this, some negative pressure is created within the system.

When PEX tubing is used, the tubes are pressed into fittings at the fixtures. To my knowledge, no crimping of the fittings are required. I've wondered if a negative pressure can, in some cases, cause the PEX tubing to loosen from those fittings, which in turn may lead to leaks at some point in the future that may not be noticed until severe damage and/or mold buildup is noticed.

Edit: Let's assume that the system in question has fittings that do not require crimping, if only because those that do would, presumably, be less prone to leakage.

  • Whether crimping is required or not depends on the fitting type. Is this a hypothetical question or are you experiencing leaking? – The Evil Greebo Aug 13 '18 at 13:26
  • @TheEvilGreebo, it is hypothetical. Whenever I've had occasion to drain my plumbing system (replace PRV, water heater, e.g.), I've always opened all our faucets. I'm fairly certain ours is remote manifold, so I'd need to be sure to open each faucet at the end of each manifold. But one of my main concerns for doing so was to ensure none of the PEX fittings came loose. – BillDOe Aug 13 '18 at 19:10

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