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Kitchen sink U bend fitting and leaking sink

Postby nl1_uk » Sun Apr 03, 2022 7:32 pm

Hi all - I've just replaced a u-bend under the kitchen sink with a kit, and am having a job fitting it to the bottom of the sink without leaks. I've tried tightening, by hand, with a wrench a little tighter, without ptfe, with ptfe, with 'lots' of ptfe. All is ok when just running a tap, but if the sink is filled, and then the plug removed, it leaks like crazy from the big 'nut' that screws onto the threaded pipe coming down from the underneath of the sink. The rubber washer is good as that was part of the new kit. Am I doing something fundamentally wrong? Any help appreciated! (see pics)
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Simply Build It

Postby stoneyboy » Tue Apr 05, 2022 10:19 pm

Hi nl1_uk,
Sill question first - is that a split in the waste section directly under the sink? It’s not clear whether the joint you are having problems with is: a flange fit (if yes use a liberal amount of silicone mastic on the rubber seal) or a ring seal on the outside of the pipe (in which case make sure the taper is located correctly before you fit the nut). If not a tapered rubber seal again use silicone mastic.
Regards S
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Postby nl1_uk » Wed Apr 06, 2022 7:52 am

@stoneyboy - Thank you so much and I cannot BELIEVE I didn't spot that!!!! I didn't for one minute think that 'mark' on the fitting could be a split, and I'd been concentrating so much on the thread/tape. Pretty sure that's the issue, as I can push a nail into into that 'mark', so I'll get a new one today. (Sometimes it's good to take a step back and 'think outside the box' a bit, eh. Thanks for spotting that.
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