I got to ask what is a bellie/sag ? we live on a slab, and the pipes are cast iron and tile after going a few feet out of the house. I know of some of the house here having orange burg ( a tar raped paper, bad stuff as it collapses in after years of us and tree roots do a real number on it.
"Belly" on a drain/sewer will be a constant problem. The "belly" is a low spot where the drain has flattened or even sagged slowing the waste water and eventually causing stoppages, 1/4" per foot is the typical grade of a sewer line. "Orangeburg" in my understanding was a war-time/post-war material used because of shortages caused by the war effort. Here in Cal. most of the o-burg has been removed. erik