I recently purchased a home with an overhead sewer system, after a few days I noticed water in the cleanout outside. Is this normal? Or will I have to rod out the sewer? There is no water coming back in yet, but not sure if the problem persists that it won't come in! Please hurry before problems begin. Thanks

There should be no standing water in a drain line. If you are not getting a backup then it's a partial clog which will get worse. I'd rod now.

Hi James and Welcome to The Plumbing Page. At AskMeHelpDesk.com.
Bob's bang on! You have something laying in the bottom of the sewer line preventing full drainage. This can only build up and get worse. Snake the sewer from the cleanout. Good luck, Tom