Water supply line cap leaking even when tight
Standard screw-on caps often fail to completely seal hot and cold water hookups, allowing water to continue leaking out. Even when these caps are twisted on as tightly as possible, the constant dripping wets the floors. This persistent leaking ultimately discourages people from using connected appliances like washing machines while the lines are capped.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Using 3-8 inch compression caps to seal off the water supply linesDid this help you?
- 2Twisting the provided cap as tight as it can goDid this help you?
- 3Switching to a brass hosebib capDid this help you?
- 4Verifying that a rubber gasket is actually seated inside the capDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Shut off the water drain it down and you should be able to undo the connections there will still Be some water so have a bucket and some sort of rags and they sell 3/8 caps that can be spun on and tightened to hold the water.”source ↗
“My landlord gave me a little cap to go over the hot water hookup, but I’m gonna be honest it does very little in way of stopping water coming out of it.”source ↗
“I have this cap twisted on there as tight as it can go, but it still wettens my floors and discourages me from using my poor little washing machine.”source ↗
Where this came up
People with this problem also raised
- 8How do you seal a leaking coolant hose fitting?
- 2Should an open indoor plumbing pipe be capped or left open?
- 127How to fix a leaking water pipe in a tight space
- 3How to keep a drain hose from popping out of a PVC pipe
- 2Where to put a hose clamp to prevent a leak
- 4How to cap a copper refrigerator water line without a shutoff valve