There are a few places you can look for the main drain cleanout. One option is to check the front or back of your house for a grate in the ground that has a cover on it. If you open up the cover, you should be able to see the drain pipe and might even be able to clear any debris from inside of it. Another option is to check your basement for a large, circular opening in the floor that leads down to the drain pipe. Finally, if you're not able to find either of those things, you can call a plumber and they'll be able to help you locate it.

The main drain cleanout is usually the closest one to your home. It will be a PVC or metal pipe sticking out of the ground with a cap on it. If you can't find it, try checking your basement or crawlspace. There's also a good chance that it's buried under some landscaping, so you may have to do some digging to locate it. Good luck!