So for about a week, I had ants in my bathroom sink. Every time I'd go into the bathroom, there would be ants crawling around the basin of the sink, and on the countertop. I kept trying to figure out where they were coming from. There was no trail of ants coming from the grout, or behind the mirror, or even falling from the ceiling. Finally, after a few days, I found out that they were coming from the sink drain. It's kinda weird because you assume that the drain only goes one way... down. Weird, considering how the ants would be constantly bombarded with water coming down the drain all the time.

Anyways, I had to figure out a way to get rid of them. Initially, I just closed off the drain. That sorta worked, but it got kinda annoying having to remember to pull the stopper up each time I left the bathroom. Plus, they started just coming out of the drain release hole at the edge of the sink. I started to read up on ways to kill ants. A lot of people said that they used Sweet-n-Low sugar.
 

Apparently, sugar substitutes have Aspartame in them, which is not harmful to humans (thankfully), but cannot be metabolized by ants. Ants eat it because it seems like sugar to them, and then they die. So I figured, what do I have to lose? I poured 3 packs of Sweet-n-Low in and around the sink drain. When I came back a few hours later, there were the ants, going crazy on the "sugar". Later that night, I washed everything down the drain.

It's now been two days later and I have no ants anymore. Yay!