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I recently went out of town for 10 days so I decided to turn off water to the house. Not from the main because I want sprinklers to run, just the water that goes in the house. I also tried my best to drain the water as much as I could before I left for my flight.

When I came back, I turned on the water. When I flushed I noticed a weird banging sound coming from the WC. It may be the air bubbles trapped in the pipe. The sound came from every toilet (3). The sound was gone after couple of flushes. How can I prevent trapping air bubbles or releasing them gently so I can safely flush or use the faucets without hearing those air sounds.

  • After I flushed each toilet, the sound does not come anymore but I am asking for future references.
  • There is nothing wrong with my water line, I just turn it off and try to drain the pipes when I go on extended periods of time.
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  • @JonCuster I have had to clean up after a toilet supply line split at the plastic tank end. Four inches of water in an entire commercial space. When my insurance company wrote the policy on my house, they said half of what they pay out is water damage, so when I had some plumbing fixes to do one of the changes I made was putting a ball valve on the basement wall for the main in to the house, with continuous PEX-A from it to the street and no fittings.
    – KMJ
    Jun 26, 2023 at 21:46

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When you drain the plumbing, you're introducing air bubbles. There's no way around that - the water has to be replaced by something, and air is the easiest substance to use since it's free and all around us. When you refill the system, it's going to push the air in to weird places. About all you can do to clear that air out is use all your plumbing fixtures to get the air out of them. Any other solution such as adding bleed valves would be expensive and complicated, and likely not worth it. My suggestion: learn to think of the banging sounds as your reward for preventing the risk of a massive water leak.

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  • Thanks @KMG! So little banging and air in the pipes is not too bad and it will not mess up the pipes etc.
    – john doe
    Jun 26, 2023 at 17:33
  • A little banging should be fine. If it sounds like a tick-tick or pop-pop-clunk noise it's almost certainly just the air bubbles working through. If the banging sounds really loud, you might be short on water hammer arresting, which is a problem generally. But if that's the case you'll be getting water hammer noises at other times as well.
    – KMJ
    Jun 26, 2023 at 17:49
  • Also: if you don't want the banging sounds, skipping the drain is the easiest way to make them stop. You're still quite protected by having the water off and it's less work all around. I wrote my answer to your question though, not to the question you didn't ask about if this made sense to do.
    – KMJ
    Jun 26, 2023 at 17:50
  • Thanks! My only concern for not draining the pipes was that there was still so much water in pipes even after closing the shut off valve that it can still cause a lot of damage. Thanks for the advice. Really appreciated.
    – john doe
    Jun 26, 2023 at 17:58
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    @johndoe I wouldn't want to find out there was a glitch and it ended up dry firing, and flipping the breaker is silly-easy to do. But then I don't drain my system, so I do use vacation mode.
    – KMJ
    Jun 27, 2023 at 15:04

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