Dennis,
Have you tried calling the Spokane Building Department and asking one of their Inspectors? Had these houses been converted from septic to sewer systems? Did either of the 45’s have cleanouts and did there appear to be any reason , like clearing an obstruction, for the 45’s?
By the way I gave you a Green Square for making me think and dig through my references, while looking for this I came across things I had forgotten or didn’t know, a good learning experience.