The house is in Orange county California, it sits on a slab 2 clean outs are on the west side of the house, how do I locate the main sewer line, would it run on the outside wall or from under the house?

We will try to move this to plumbing where some plumbers will see it. You sewer drain will not go through a wall if you are on a slab. It is under the slab and exits under the house probably on street side but not always. Check with the local building department, their plans will show where it was planned to be but not always 100% correct.

Hi Baracuda... a typical OC house on slab will have main sewer pipe running under the slab and just about in the middle of the house. I assume you have 2 car attached garage facing street. Some builders used to put a clean-out cap someplace in the garage floor or driveway. Look for a round, concrete cover, about 10" in diameter. Otherwise, to locate sewer line, plumber will have to use Pipe Detector / Locator device to spot it for you.

Question: what's the reason you are trying to locate the sewer line ?

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how do I locate the main sewer line,

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My company kept a set of "AS-Built" prints on all our new construction. Contact the plumbing company that did the installation and ask them if they could furnish you with a set. Good luck, Tom