Recently, the bathtub in my daughter's bathroom started draining very, very slowly. I bought a bottle of Draino from the local store, followed the directions on the bottle, and after a hour I went to flush the tub. The water now drains faster than before, but as soon as you turn the water off and the tub starts to drain, I hear loud gurgling sounds from the drain as the water leaves. What could be causing this loud noise? My house sits on a slab foundation, so I can't check the pipes. Any ideas folks? FYI, the house was built back in 1996.
You most likely have an obstruction in the pipes. There are a couple of easy things to try: First, use a wet dry vacuum to try sucking that obstruction out from the drain. This approach sometimes works. Another idea is to attempt using a mechanical snake to clear that drain. Snakes are available in a wide variety of shapes and sizes, and can be purchased at any home center. They work if the obstruction is relatively close to the drain.
Beyond that, you need to get a professional drain clearing service. Do your homework - hire someone reputable with good reviews. Bathroom drains are very susceptible to clogs from hair or soap scum, so dealing with one is really only a matter of time. In the future, though, reconsider using Draino. Its results are iffy and potentially dangerous, and in some cases can damage pipes.
If all these steps are taken and the drain's still noisy, the issue might be that the plumbing system is not vented properly, and the gurgling is the result of it being starved for air. This should be addressed by a plumber.