This thread reminded me of something I posted on the subject almost two years ago.
I used to live in a house that had a strange gurgling tub, too. One morning, I went in for my early shower (this was my freshman year in high school), and there were at least two dozen squirming larvae in the tub. Greyish-brown, maybe an inch to an inch and a half long, thin and wormy with a hard shiny exoskeleton, like small millipedes.
It was weird, but I’m not creeped out by bugs, so I washed 'em down the drain and showered. Next morning, they were back again. Clearly, they’re living in the plumbing or under the house or something, and coming up the drain during the night. I washed 'em down again and poured bleach into the drain. That should fix 'em, I thought.
For a while, it seemed to have done the trick. But then maybe a week later, I found even more of the little squirmers waiting for me first thing in the morning. At that point, what was making my skin crawl was not so much the general thought of the bugs, but what would happen if someone didn’t look into the bathtub before stepping in, and crunched the little guys with bare feet.
That’s not the worst part, though. The worst part is that a couple of weeks later, after washing the bugs down the drain had become a routine, the tub developed a strange gurgle. First time, it happened to someone else, but it kept doing it afterward, so we all got to experience this lovely moment. You’d be in the shower, the drain would start to slow down, and you’d hear heavy burbling and clanking from the pipes.
And then the squirming millipedes would come back up the drain and swirl around your feet.
All together now: Ewwww.
We had a guy go into the crawlspace and take stuff apart, and after that, no more wormies. I have no idea what he found down there, but, at least at that time, I didn’t want to know.
Sorry if I gave any of you entomophobes additional nightmare material, but I just had to share.
(link to old thread)