I bought my house 2 years ago, and right after I moved in I noticed the previous owners had the hot water to the dual master bathroom sinks shut off. I turned it back on, and the sinks immediately started backing up into each other upon use and draining VERY SLOWLY.

I put Drain-o down them every few months, which temporarily clears the issue so I can use the sinks, but they still drain slowly. The Drain-o has eaten through one of the fittings under one of the sinks. I won't be doing that again.

There is one roof vent for both sinks, and the toilet in the bathroom works fine. The shower is unfinished. Each sink has a visible P trap before the plumbing disappears back into the wall. There is no visible clean out. Is it possible a fitting was installed backwards? I think the clogging is a symptom of an installation problem, but I don't know exactly what the problem is. Please help!

Your problem is a partial stoppage of the drain branch serving the two sinks. The drain will work once it is cleaned properly.

It's been snaked with temporary results. Is there another, more effective way to clean it?