Found the leak. It is in fact the metal hose from the shut off valve. This is going to be a job and a half. There is no space to work around the tank.

Here is a picture of the valve. Do I need to replace the whole thing with the water supply line? How would I go about doing that?

It looks like the hose is part of the valve?!? I've never seen that before (but then again, I'm no plumber)

Google "replace toilet water valve" and it will come up with all kinds of videos that you can watch to see step by step on how to replace the whole thing.

Yea the hose was attached to the valve. I went to Home Depot and took the old valve so they can give me a replacement. The replacement valve goes on too loose on the copper pipe in the wall. Even with the old nut off the old valve placed onto the new valve and a copper ring inside, it still slides on loosely onto the shaft from the wall.

So I replaced a valve and now I have a very slow leak coming from behind the packing nut. Maybe 1 drop every 20 seconds or so. I tightened the nut giving it maybe a quarter of a turn, but it still has a slow leak. Should I tighten it some more? Or is there another solution?

Thanks.

Time to call a plumber.

What was the pipe made of that sticks out of the wall? There are different compression fittings for copper vs. iron pipe and the diameter is different, and the Home Depot guy may not understand the difference. I've also found that the small boxes may (which open easily) may have some mismatched or pilfered parts that don't really match the valve. Maybe they sold you the wrong compression fitting.

Did they also show you Sharkbite fittings, which may have been in a different part of the store? I know you can get all kinds of repair fittings from Sharkbite, but I've never looked for a toilet valve. They are high quality fittings that are good for repair, although too expensive to use for a larger job with many fittings.

If the pipe in the wall is copper it would only take a plumber (or you) about five minutes to solder on a copper fitting with threads.

Bruce

What was the pipe made of that sticks out of the wall? There are different compression fittings for copper vs. iron pipe and the diameter is different, and the Home Depot guy may not understand the difference. I've also found that the small boxes may (which open easily) may have some mismatched or pilfered parts that don't really match the valve. Maybe they sold you the wrong compression fitting.

Did they also show you Sharkbite fittings, which may have been in a different part of the store? I know you can get all kinds of repair fittings from Sharkbite, but I've never looked for a toilet valve. They are high quality fittings that are good for repair, although too expensive to use for a larger job with many fittings.

If the pipe in the wall is copper it would only take a plumber (or you) about five minutes to solder on a copper fitting with threads.

Bruce