Everytime kitchen sink water is used it leaks through in the basement (shown in the picture below). I wonder if that can be fixed by applying silicon around or it's something bigger of an issue that might require professional.

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Update 1 I followed up on suggestions from feedback and confirmed that it's leaking from the original place. Also tried putting pressure on the pipe to see if water can leak more. When applying pressure like this (see the second picture attached) the leak stops. That might mean that there is crack in the pipe? Silicon can be a solution albeit temporary one, right?

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  • 1
    It looks like you have a reducer adapter there. Could it be leaking from the outer edge of the water in the adapter. Check and make sure the pipe is not crack somewhere in the down drain and the reducing adapter. If the pipes are crack free, then I try and coat the complete flat area with silicon. Commented May 21, 2020 at 1:21
  • Programmer66 thanks! i updated the question. your solution is still viable?
    – mike123
    Commented May 21, 2020 at 3:00
  • When pushing its stops leaking, indicates that there is a small gap in the sealed joint on the opposite side of the pipe where you are applying pressure. You're lucky, there is a removeable joint connection in the pipe. I would try loosing the connector, slide the connector up, and gently move the lower pipe section in a small circle and see if the seal can be broken where it is leaking. If successful, you will be able to remove the section and repair or replace. Commented May 21, 2020 at 5:43
  • If the above doesn't allow you to remove the lower section, it appears you have enough 4" pipe below the cleanout to do a proper repair by cutting the pipe at the bottom edge of the cleanout and replacing the whole lower section below the connector. the cleanout, reducer adapter and the 45's. Just make sure all the joints are clean and smooth before gluing up the joints. Watch a couple of YouTube video for the proper technique. If unsure about DIY, then lightly sand where it is leaking and just apply silicone completely around the flat area and above and below for 1/2". Commented May 21, 2020 at 6:05
  • 1
    If the leak is at the rubber hub (fernco) silicone sealant may be your best bet the rubber of the fernco and silicon will bond and help in the seal. I would want to clean it , loosen the pipe clamps move it and wipe the the area down there are normally ridges in the rubber fill a couple of those with silicone on each side and tighten the clamps. Depending on the type of pipe (cast) I always use silicone with the hub when installing and never have problems.
    – Ed Beal
    Commented May 21, 2020 at 13:12

2 Answers 2


Your drain might be backing up , a 1-1/2 or 2” sink dumping into a 4” drain should not have any back pressure . I see your arrows but can not tell why it would leak there , I would try a silicone sealer . If there is not a vent close to the sink this could cause issues but at the point where the size jumps would be a new one for me. If you run water for a few minutes will the leak get worse? How long after turning off the water will that spot leak? If it leaks for a while after stopping the water flow I would want to run a snake down the drain and see if it is backing up.

Added per op request; On fernco or no hub rubber connectors I regularly use silicone sealant (cast iron and concrete always) I would loosen the pipe clamps move the hub and clean it the I would add some silicone and retighten the clamps. This will help seal the rubber for the life of the coupling.

  • 3
    It looks like there is a cleanout access on the 4" drain. It would be easy to take that off and poke around, or snake from there.
    – Willk
    Commented May 21, 2020 at 1:57
  • The leak starts almost right away when water is turn on, and stops as soon as water turns off. I'll run the test again shortly to making sure that what it is
    – mike123
    Commented May 21, 2020 at 1:58
  • Ed Beal, I have updated the question with the update 1, there is seem to be a crack?
    – mike123
    Commented May 21, 2020 at 2:58
  • Wiillk, there is another access from up top, but it might not require .. the pocking around, partially because i wouldn't know how ...
    – mike123
    Commented May 21, 2020 at 3:04
  • I'd upvote for mentioning that the drain shouldn't have any back-pressure, but, IMO, adding silicone sealer is just wrong in the general case as advice to a DIY person who doesn't really know what they are doing (which is how future visitors will be reading this answer). It might be appropriate after resolving the primary issue that the 4" drain is backing up. It also might be a temporary solution, if the user can't get the primary issue resolved in the very near future (e.g. they may not be able to get someone out while staying at home). I'd suggest more clarifying language.
    – Makyen
    Commented May 21, 2020 at 17:40

Silicone sealants are basically never a fix for leaky pipes. They almost always fail in that application, usually in a relatively short period of time.

One common possibility to be on the lookout for is that "where you see the water" may not be "where the leak is" if it's running down the pipe in a thin enough stream that you don't notice it, perhaps on the side where it's harder to see. When testing for the leak, try wrapping a paper towel or something around the pipe higher up to check for wetness coming from above - you may just be seeing a puddle at the bottom of the pipe that comes from a higher level, even the trap on the floor above.

  • Ecnerwal, I tried your suggestion and updated the question. Thank you!
    – mike123
    Commented May 21, 2020 at 2:56
  • Rubber hubs need silicone to seal in many cases and I have never had that seal fail.
    – Ed Beal
    Commented May 21, 2020 at 13:13

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