removing galvanized pipe

We have been in our house for almost 8 years and just a few weeks ago have started having a very foul smell coming out from under the counter in our master bathroom. It is definitely a sewer smell and is VERY strong. It is not constant, however, and seems to get worse when it is cold outside (though the sink is not on an outside wall). The bathroom is close to our laundry room and we had one plumber tell us he thought the problem was the washer pulling strongly on the water line and getting all the air out of the bathroom sink trap. He told us to run water down that sink drain when we use the washing machine. That hasn't helped and there doesn't seem to be a strong relationship to when the smell is bad and when we've run the washer. Any help we can get before I call another plumber and waste more money would be greatly appreciated!!!

Both of the faucets in my bath rooms will not turn off all the way. I have had the seals replaced and even the stems. But after about a year they begin to leak again. I know that you are not supposed to tighten the handle too much, but that is the only way I can slow the flow of water. Is there anyway to adjust the handles so the water will shut off completely? Do I need to turn the water off at the main to do this, or if I remove the screw in the handle will I get a gusher? I am thinking of replacing the entire unit, but I need to get water turned off until I can afford a decent plumber. Can you offer any step by step instructions that I can follow..My hubby is a carpenter..and you never give a carpenter a wrench..haha..thanks for your help.