Technicians arrived on site to investigate report of foul smell coming from garage and driveway. Upon further inspection technician found the smell to be emanating from the crawl space vents. Technician popped off vent cover and use flashlight to inspect crawl space and found very large pool of sewage. Technician inspected crawl space access at other end of home where an add-on was placed. all plumbing in the add-on was done in ABS and appears to be on a separate lateral. All plumbing where the location of the leak is is cast iron. Technicians recommend client use a restoration company to pump out all sewage from crawl space. crystal blue plumbing heating and air will then come out and either perform a spot repair or a full sewer repipe underneath original home. Technician provided homeowner with business card and membership pamphlet. Client stated she had a couple more people coming out to take a look and requested we leave the crawl space vents off for better access.