I recently changed our sink drain 'S' trap for a bottle trap, and since then the sink 'glugs' each time water is drained. Once the water has finished draining the noise begins. At first, it makes a single glugging noise about once every 15 seconds and this goes on for up to 10 minutes with the frequency getting gradually less. The old 'S' trap never made this sound. I wonder if bottle traps are notorious 'gluggers' or perhaps something else is going on? The sink drain does not share with any other item such as a washing machine or dishwasher.
S traps normally feed into a vertical waste pipe whereas with bottle traps (like P traps) the waste is always horizontal.
My first reaction is syphonage and I'd try an anti-syphon bottle trap. However you say that the S trap didn't do it but S traps are prone to syphonage so its confusing. Perhaps you should go back to an S trap?
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