drain

This could be real easy. First look at the sink and see if there is any water in the p-trap. The p-trap is that “U” shaped pipe under your sink. It provides a great service. It fills with water and forms a gas tight seal to the main sewer system. Many times I’ll go out and find a shower or a sink in an area that is rarely used and the trap will be dry. I’ll turn the water on, fill the trap and the problem is solved. So obviously that is where I would start.