Is it mandatory/recommended to apply cement on all threaded parts of a P-trap. I need to install a new one, and am wondering if I also need to get a plumbing cement. Also, if I purchase a P-trap with cleanout, is a cement necessary on a cleanout nut? (I would not, because otherwise the whole purpose of cleanout is undermined, whenever you need to clean the trap, you're going to have a hard time trying to unscrew it/)


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    You do not use cement on the threaded parts of a p-trap. The threads compress the joint; the seal is effected by rubber or plastic seals or faces. – Jim Stewart Jul 12 at 1:11
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    There is also virtually no "pressure" on the drain line, so it's easy to seal with compression gaskets, included with the new trap. Don't glue it! – George Anderson Jul 12 at 1:35
  • @JimStewart That there's an answer, not a comment! – FreeMan Jul 12 at 1:37
  • @GeorgeAnderson That there's an answer, not a comment! – FreeMan Jul 12 at 1:37
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    Cement doesn't just 'act' as glue. It is glue. Most good plumbing cements form a 'solvent weld' which actually chemically 'melts' the parts together. – brhans Jul 12 at 19:50

You do not use cement or any sealant on the threads of a p-trap. It would not do any good and would bond the threads and so prevent adjustment. The purpose of the threads in these drain elements is to compress the joint. The seal is made by rubber or plastic ring seals or the faces of the two parts of the p-trap.

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