I have had a backwater valve installed recently. But I did not think about the fact that I have a drain at the bottom of the stairs right outside the basement door. Would that drain be connected to the drain in the basement? If that is the case the backwater valve would be useless during a rainstorm since the water draining down the stairs would back up in the basement drain. Maybe I am just being paranoid. The plumber would've warned me not to install it if that was the case. I haven't been able to contact him recently.

In my area, Tampa Bay, it's illegal to discharge anything but sewage and gray water into the sewer system. However, since it's the closest and the easiest way to go, there's no doubt in my mind that the outside drain's connected to the sewer.I would install a floor drain check valve,(see image) in my basement floor drain. Click on; http://www.plumbingsupply.com/floodguard.html to check out "Flood Guards" Easy to install, they will prevent basement flooding. Good luck, Tom

Thanks, so does that mean that I have wasted money on installing the backwater valve?

If all you have coming off the main is the stairwell floow drain aqnd the basement floor draib the answer is yes. Regards, Tom

Well actually I've got a toilet, a shower, and of course a couple of sinks down in the basement

Angelo

Then, to give you protection for the basement floor drain and the shower the check valve should have been installed upstream from the stairwell drain.
But wait! How do you know the sewer won't carry away all the water the stairwell floor drain collects? And even if you get basement backups you can still install "Flood Guards" on the floor drain and the shower drain. You have two options open. (1) install Flood Guards as a precaution,**or** (2) wait until the next heavy rain to see if you really need them.
Good luck, Tom