I have noticed a trend in posts from people with concerns about a stink from the sink. If it is isolated to only one sink and the sink has an overflow hole, it may be related to mildew, scum and build up in the overflow or even in the tail piece.
If you have a pop-up drain and can remove it you can look down the drain to see if there is a lot of soap scum, hair...well, just about anything that can stay moist and begin to stink. If it is clear or after you clear it, rinse water down the drain and flush water through the overflow with a detergent to clean and clear mildew/bacteria/scum from the drain.
Instead of filling the sink until it overflows to get water down it, I have used a funnel and poured a mixture of about 1 part bleach to 15 parts water down the overflow.
First things first, though. Is it only one sink or isolated to a certain area of the house?