Leak under sink

Hello everyone,

I am a new homeowner and very new to diy plumbing, so forgive my lack of vocabulary, etc.

Some time ago I discovered a small leak beneath my sink, on the incoming cold water pipe connection. I was able to fix it by redoing the connection with the sink line (I used pipe thread tape) and retightening all the bolts, although it took me a few tries.

Recently the problem has resurfaced, and this time I haven't been able to fix it. Does anyone have any ideas? I'm attaching a picture of the connection - the water seems to be coming out of the big gray plastic thing at the bottom of the connection.

I did install a new sink several months before the first leak appeared; I don't know if that was related.

Thanks in advance for any help!

There is no reason to have all of those reducer adapters (all waiting to leak) on that shut-off valve. Get another 1/2"-to-3/8" compression fitting type shut-off valve, replace the one(s) that is on there, attach the stainless steel flex hose (or a newer longer one if necessary) and be done with it. Neither the 1/2" compression fitting end of the valve or the 3/8" flex hose end of the valve need teflon tape. The compression ring ferrule seals that end on the straight copper pipe, and the flex hose should have a rubber seal built in.
Good luck!
Mike

Also, you don't need stop and waste valves under the sink. Just get standard cut off valves. A plumbing shop will know what you need.

If the valves work and you want to use them to shut off the water for working, just solder delta adapters on the top of the valves that are there. They go from 1/2" cc to 3/8" compression.

I was able to fix this today - thanks for all the help everyone!

I cut off the pipe below the old valve and put in a new shutoff valve with a compression fitting. Ended up needing a longer (30") flex hose as well.

Seadogg said:

... the water [seemed] to be coming out of the big gray plastic thing at the bottom of the connection.

Click to expand...

I could be wrong, but I believe that gray nut was half of a Qest fitting with a reducing bushing screwed into it and the bushing was not providing a good seat for the sealing ring.

It looks like Rube Goldberg plumbed that up... You did the right fix!