How a belly forms and what it does
Front Range clay swells when wet and shrinks when dry. Over a decade that movement can drop one section of a sewer lateral below grade. Water sits in that dip permanently, solids drop out of suspension, and the low spot becomes a collection point.
Recognizing a belly from the symptoms
Repeated backups at the same interval, on a house too new to have root problems, is the signature. Camera footage confirms it by showing standing water in an otherwise clean pipe.