Does anyone know how to fix a small leak in a bathroom basin? There's a small pool of water just under the bend in the basin pipe. The faucets don't leak. I've checked under the basin, and both copper pipes are dry. There's water visible around the top of the basin pipe, where it joins the basin. It's not dripping much, but I wipe up the pool and it forms again. I'm worried it might become worse.

As far as I can see, there's no sealing material around the top. Just the screw-on joint/connector. Any suggestions gratefully received.

The first thing you must do is determine the source. It's leaking from the drainage section. Take a piece o9f toilet paper and start from the top. Rub around each joint and look at the TP. The first sign of moisture is the joint you must tighten. Good luck, Tom

Thanks, Tom.

I've just done as you suggested, and the source of the water is right at the top of the basin pipe, where it meets the basin. There's a collar around the pipe which sits right under the basin. I can see moisture above the collar. Do I just try and screw the collar so it moves up against the basin? Should this form a better seal? I'm really not sure how these things work.

There's a rubber spud washer under the collar. Snug up the nut and see if the leak doesn't stop. Good luck, Tom

"There's a rubber spud washer under the collar. Snug up the nut and see if the leak doesn't stop. Good luck, Tom"

Thanks, Tom. Excuse my ignorance, but I've never heard of a "spud washer" before. By "snug up the nut", do you mean bind the thread with plumbers' tape (assume it's on the pipe itself) or something else?

Sorry I'm not familiar with the terminology used.

What he means is for you to use a wrench on what you called a collar, if this collar has some flat places for a wrench to fit on, if it does fit and you can turn it, turn it Clockwise as you are looking up at it. If this does not turn easily my suggestion would be to replace the complete thing that goes through the basin and down to the P-Trap. This assembly is called a pop-up assembly and can be purchased at a major hardware store at a cost of around twenty dollars. Even though it may look forboding to you it is really not that hard. Turn the collar below the basin counter clockwise to take it off. If it will not turn without turning the whole thing then you can use two screwdrivers stuck into the holes of the drain hole in the basin, that is after you take the stopper out. Make a cross like contraption with the screwdrivers with one pressing against the other as you try to unscrew the collar on the bottom of the basin. Now one more thing that you may run into is the little chrome ring in the bottom of the basin, on some Pop-ups this little chrome rings has to unscrew and then the rest of the Pop-up drops down. So if the collar does not screw all the was off lift the entire pop-up until you can get a pair of pliers onto the chrome ring and unscrew it.
If you get this far and are replacing the new pop-up, you will want to use a small amount of putty under the new chrome ring in the basin, tis is to seal the ring to the basin so all of the water will not seep out of the basin if you are soaking your unmentionables in it.
I hope this helps.