remove the hose from the valve to the toilet, then you'll know if the leak is at the compression fitting on the valve or from the tank. The leak should show up pretty quickly.

Ok, just shut the valve off at the wall and removed the hose that comes from the tank. I'll see how long it takes the towel to get wet, but I really think it's wet behind the valve. How to fix that? It has to be the valve connection to the copper pipe. The valve is new, so I have to think the 1/4 turn shut off feature is perfect. I've had those fail before, but it was after many years of super hard water abuse.

That fitting should not have teflon tape on it. On the other hand, the teflon tape shouldn't hurt anything either.

Sweating means soldering.

I just removed that teflon tape from the plastic-metal end. I've replaced several of these and never seen one that was soldered. Doesn't that make it such that it always has to be replaced if there's any issue? If pipe compound doesn't do it, I'm gonna be worried. What else can I do here?

That is a compression fitting on both ends?

Put some pipe compound on the leaky side, like Loctite 567.

Not on the threads, on the ferrule and the pipe.

Sweating means using solder to seal the joint or fitting.

How to Sweat Copper Pipes and Fittings | PlanItDIY


What you have is a compression fitting. They work fine, as long as you dont over tighten them. If you did, for $5 try a new one. Looks like you dont have much room but try and make sure the copper ring is in a different place than before.

You can remove that echelon if you need more room and just mud around where the pipes comes out of the wall.

If it is leaking behind the wall, your going to have to chip the drywall away from around that pipe and have a look.

You could also solder to the 1/2 pipe coming from the wall...

Getting the old ferrule off was a real task. I had to Dremel off the nut first to then get to the ferrule to Dremel it off. I really don't want to do that again and risk slicing into the pipe, which would be disastrous. I think I'm gonna go with pipe compound.

1990c4s is correct. U have a compression fitting on both ends. You need a fitting that has compression coming out of the wall (connects to the pipe)and a the correct threads for that hose. THEY ARE DIFFERENT.

Are you saying I have the wrong parts? They match the old parts perfectly. The way this connects to the pipe in the wall is with the large nut and ferrule. What else is there?

Give me a second

The compression valve come in 2 styles
Compression on both sides
Compression on one side(compression from the pipe) and a hose barb on the other.

Since you have used pipe dope on your hose is because those are compression threads and not the correct threads for that hose.

I'm looking for pics on the net

The hose fits on that valve perfectly. All threads match and feel right. And the leak isn't at the hose anyway. The leak is where the valve connects to the copper pipe.

I'm guessing the OD of copper pipe is deformed enough that the compression fitting isn't sealing. Shark bite makes a fitting that may seal better.
SharkBite 1/2 in. Chrome-Plated Brass Push-to-Connect x 3/8 in. O.D. Compression Quarter-Turn Angle Stop Valve-23036-0000LF - The Home Depot

OK, Than your going to have to take off the valve and and try again.
You might need another ferule and or shorten the pipe. It has worked for me lots of times, to just move the ferule (closer to the end by a small amount) then retighten

Here are some pics
https://www.google.com/search?q=quarter+turn+valve+home+depot&espv=2&biw= 1137&bih=725&source=lnms&tbm=isch&sa=X&ved=0ahUKEw jw9pTRxInMAhXLSyYKHU2PAvkQ_AUIBygC&dpr=0.9#tbm=isc h&q=how+does+a+compression+fitting+work&imgrc=_

Dad911 makes a great suggestion. Those types of fitting have saved me lots of times when it too inconvenient to sweat a pipe.

Ok, thanks. I'll see if I can find that SharkBite one. Should I also get some pipe compound since I'm going to have it all apart again?

with the valve Dad911 suggested you wont need it. Please check inside the hose to see if the threads are not damaged. You should NOT need pipe dope on those threads anyway cause there is a rubber washer in there that presses against the valve to prevent leaks

Yeah, the hose is not the issue. No leak there. The leak is coming from metal on metal, likely the ferrule on the copper pipe.

That hose should only be hand tightened, thats why they are not made to put a wrench on it. When you go back to the store, take the hose with you and when you find the click-on valve, check to see if your hose screws on with ease