Where should I tap into water line to run to a guest house. Is water usually located near cleanout

Water is easy. You would tap into a convenient location so the distance is as short as possible. Not sure about your "cleanout" comment, that's for a drain. BUT, how are you going to drain and vent the guesthouse?

Main house cleanout is closest drain to guest house . Was going to tie into it for drainage. Closest location for water is across property at water hose spicket

To prevent freezing, the water will have to be located below the frostline, wherever it is in your area. I would run the water to a pitbox, install a shut off line and then run into the guest house. How are you going to bring the water in? Underground? You will have to cut some concrete to get the drains out or is this on a crawl space? You will need a vent in the guest house. Are you going to pull a permit? They will help you with the layout requirements if you do. You will most likely need a 3 or 4" drain to the main drain, 2" sink drains to the 3" and a 1 1/2 or 2" vent, possibly an AAV if allowed. How are your handyman skills? This is not an easy DIY job unless you know the plumbing codes for pipe sizes, slope etc.

I plan on running my water line 20" down ,so not to have freezing issues . I'll use right materials . I'm just trying to find out if there's any other place to tap in the water because the guest house and water meter are at opposite ends of my property . And my sewer pipe out [4"] runs right by guest house , so I was hoping water line might be there too. My property diagram doesn't have my water line routes. Thanks guys