I removed our toilet to paint behind it. There is a VERY slow leak from the end of the short pipe that leads from the valve itself to the toilet. I have tightened everything and the minimal leak is still there. I can get a plumber in tomorrow. In the mean time, it seems someone must make something that would seal this. The nylon nut could be connected to something and I should be able to tighten it and stop the leak. Googling does not help me. Is there such a device? If so, what is it called? If not, what might I cobble together to seal the end and stop the leak?
End of the fill valve that you use to turn the water to toilet on and off.
Plumbers putty. Just a small dab and coat the threads and mating surfaces. Tighten snug and let sit half an hour before applying pressure. I was told about this trick by an old time plumber many years ago. I have never had a leak in all of my plumbing endeavors. Much easier to install that Teflon tape too.
I was going to suggest teflon tape. It’s been my goto for all plumbing repairs.
I don’t find it hard to use at all. Just wrap it around the threads a couple of times.
If that hose is old, it might be a good idea to upgrade the hose to a newer one while you’re making this repair. Flexible hoses that go to toilets and washing machines often fail over time and are common sources of water damage.
When using so-called “Teflon” tape, make sure to wrap it in the right direction. It should be wrapped clockwise around the male fitting, so that tightening the female fitting does not peel up the end of the tape.
Since this is GQ, I’ll nitpick that there is technically no such thing as Teflon tape. “Teflon” is a trademark of Chemours, and they do not produce any plumbing tape. It should be called PTFE tape or thread-seal tape.
Sorry for not making myself clear. The end of the inlet tube is not connected to anything. The toilet is in the other room. I was looking for something to screw the nut into that would seal it until the plumber gets here tomorrow to replace the entire valve.
I can’t tell if that last post helped my understanding or hurt it 
If it helped it …
Could you just reinstall the toilet temporarily, until the plumber comes ? Should buy you quite a bit of time if a) I have this right, and b) the leak is minor.
??
ETA: otherwise, a lot of hardware stores stock a variety of different sized rubber stoppers. Might one of those work ?
You can get a little brass cap that screws on to the end of the valve. If you have a hardware store nearby, they can get you fixed up. If the leak is not too bad, you can just collect the water in a bowl or something. The valve may have calcium deposits or something which is preventing the internal stopper from closing all the way.
A sharkbite or similar push-fit end cap is what you want. A pipe cutter is handy to cut the pipe if copper, but a hack saw will work. There are cutters for PEX, but a hacksaw or utility knife works too.
Shut off the main water, cut the pipe immediately below the bad shut-off, and press the sharkbite firmly on the end of the pipe. Have a friend turn the main valve on while you confirm the end cap is holding. An old towel should be handy to clean up spills when you cut the pipe.
If I’m reading this right, the shutoff valve for the toilet is leaking ever so slightly, so it’s dripping from the 7/8” end of the flexible line that is usually screwed to the bottom of the fill valve on the bottom of the toilet tank. For overnight, I’d just put the end into a bucket, pan, whatever to catch the drips.
The fix does involve shutting off the house main valve so the shutoff can be repaired - usually they just need a small rubber washer, but the trick is identifying the diameter , thickness, and if it should be flat or beveled. Easy for an experienced plumber, but can be either super easy or super frustrating to us do-it-yourselfers. Sometimes it’s quicker for a plumber to just replace the entire valve as the internals get corroded.