I am trying to locate the clean out, outside my home. Do they ever have these inside the home?

Yes they do. Look at your main 4" main as it leaves the house. If it goes through the basement wall the clean out will be right at that elbow in the form of a Wye with a cap. If it exits through the floor look for a cap on the floor next to the main drain. Outside are usually 18" to 24" from the foundation but mat be slightly buried due to landscaping over time. If you find the clean out inside and you have a clog do not open the cap just yet. Get a 1/8" sheet metal screw and a 1/8" drill bit and drill. Drill a hole in the cap, if sewage squirts out insert the screw and wiat until the sewage drains or you can adequate bucket to catch 20 gallons of sewage, I'd wait.