I have installed a 3 stage water filter unit under kitchen sink. I have not been able to get it to stop leaking. The cylinders that hold the filters are plastic and screw into a plastic lid that attaches to other two filters. I used chap stick (I didn't have real petroleum jelly) to stop leaks between gasket and top of lid that screws down tightly to gasket. One keeps leaking no matter how tight I tighten. Should I get real petroleum jelly or some other plumbing product?

First off Chapstick and petroleum jelly are not in our bag, get plumbers grease. Is that gasket a large O ring, make sure there is no pinching or nicks in it. Grease the O ring and the groopve it sits in. When screwing tha caps on make sure you don't cross thread them and try to have no tension or pull in any direction.

First off Chapstick and petroleum jelly are not in our bag, get plumbers grease. Is that gasket a large O ring, make sure there is no pinching or nicks in it. Grease the O ring and the groopve it sits in. When screwing tha caps on make sure you don't cross thread them and try to have no tension or pull in any direction.

Thank you for answer. Is Great White Pipe Joint compound the same as plumers grease? I understand I should put it on the black O ring, should I also apply to the threads of the container that hold the filter and screws into the top plastic lid?

Ballengerb1-is Great White Pipe joint compound the same as plumbers grease? I understand I need to put on O ring and it's groove, should I put it on the large threads that hold the filter and screw into the lid? Or should the O ring be sufficient?

Good stuff but not in this situation. Plumbers grease can be bought ina small tube of 3 oz. The Great white would be perefect if joining a galvanized pipe with a galvanized connector, don't use it on your filter washer or the threads.

You should not have to use joint compound/grease of any kind to stop it leaking.

You should have a large o-ring. Make sure it is in the right spot. It is easy to make the big & stretchy o-ring fit in many spots... but only one spot with a flat mating surface will form a leak free joint. If I am picturing what you are describing, the o-rink should fit inside the cylinder at the base of the screw threads. It should not be resting on the threads i.e. you should be able to screw the cylinder on and have it squish o-ring against the matching flange just before it tightens up.

If you have moved the o-ring around a lot, then it may be scratched or otherwise damaged as Bob suggested.

If you are sure it is in the right spot, and it still leaks, I'd try a new o-ring first. If you end up having to use joint compound of some kind, use it sparingly on the mating faces where the o-ring fits, because you are drinking that water.

I had the same problem, the O-ring might have swelled, in my case I believe it is because I have soft water. If you put petroleum jelly or any petroleum product on the O-ring it will swell. Like RTW said, you probably need a new O-ring or you can do what I did, cut the O-ring with a razor and remove about 1/8" and super glue it back together, but still get a new O-ring as a back up.

Plumbers grease is actually inferior to food grade silicone but it should work fine. I'd try a new gasket and matbe not with the cutting, save that for middle of the night emergencies.