The bathtub won't drain. I tried two separate liquid cleansers and a plunger after blocking the overflow valve. After using the plunger, the problem is worse. There is a slight water backup when using the bathroom sink and it takes longer to drain. Should I try the plunger again and cover the bathtub overflow valve and the bathroom sink?
Thanks.

I am no fan of using harsh chemicals in your drainage system. Besides, they only seem to work in TV commercials.
You must snake the drain from the tub overflow. Put out at least 15 feet of snake. Good luck, Tom

I am most fan of using harsh chemicals in your drainage system. Besides, they only seem to work in TV commercials.
You must snake the drain from the tub overflow. Put out at least 15 feet of snake. Good luck, Tom

Diddo on what speedball1 said regarding snaking. Also, I assume your drains are properly vented? Lack of venting won't completely block drainage, but will definitely slow it down considerably. An easy way to tell is if you hear a gurgling sound coming from the drain, after you've drained some water. The gurgling noise is air bubbles going through the water in the P-trap, because the lack of venting is causing a pressure differential in your system. I always give my clients the analogy of an unvented drain being like flipping an open water bottle upside down, the water drains slowly because air bubbles are getting in. A vented drain would be like if you drilled a hole in the bottom of the bottle... water comes out fast because air comes in from above.

Thanks for the great explanation on venting. I don't believe this is a venting problem but rather a simple blockage. And welcome to the plumbing page. Cheers, Tom

Thanks Tom! I appreciate the welcome. :)