Our bathroom sink has been giving off a bad smell for over a week. It smells more like dirt, not like sewage. We've cleaned it out in numerous ways and now the water drains fine. However, vinegar & baking soda (repeated treatments) and salt & a pot of boiling water, have not helped to get rid of the smell. Any suggestions?

Is the smell coming from inside the lavatory or under the cabinet?

It seems to be coming from inside the sink or pipes - we have no outside cabinet around this sink. I am starting to wonder if there's something in the overflow drain/pipe which I've only tried to clean once, last night.

"We've cleaned it out in numerous ways and now the water drains fine."
Did you check and clean the pop-up rod?: If not try this.
Remove the stopper from your sink. Look down in the drain and you will see a rod about 6" down. Hair hangs up and fermemts on that rod. Fish it out,(ugh!) The reason you smell it at the overflow is that when you drain some of the smell is forced back out the overflow. Now pour a quart of bleach down the drain and let it set overnight. Next morning,(and this is important)flush it out with a pan of boiling water If you can'tpull the stopper out then your stopper has a opening at the base that the rod goes through so that it can't be pulled out. To defeat this and pull the stopper look under the sink and follow the pop up lever down to the rod. You will see a knurled nut. Now push the pop up knob so the stopper is in the up position. While holding the stopper in one hand, slowly back the nut out until it's clear,(You may need to free it with a pair of pliers) Careful! You don't want to pull it all the way out. Now, GENTLY pull back on the rod while pulling upwards on the stopper. As soon as the stopper clears turn the nut back in hand tight or tight enough to hold the plunger rod up. From here on in you will let the stopper ride on top of the rod instead of tying it down. Now take a bent coathanger and fish out any hair that may have hung up on the rod or the trap. After you have cleared out any hair or trash, just drop the stopper back in the drain. When I install a bathroom sink I never tie down the stopper so that the owner can check the drain without the expense of a service call You might also put a lemon in the blender and liquefy it. Pour it down the drain and let it set overnight.Good luck TOM

Dear Speedball1 - Thank you for these great suggestions. I am waiting for my husband to implement them (!) and will let you know how they work after he does that. Many thanks!!