The answer
Chronic clogs stem from fats, oils, and grease (FOG), hair/soap scum binding, flushed wipes, or root intrusion in main lines. Trade associations strongly advise against caustic/acid chemical cleaners because exothermic reactions warp PVC/ABS, corrode cast iron, ruin gaskets, and create chemical burn hazards for plumbers. Use mechanical snaking, augering, or hydro-jetting, followed by enzymatic treatments.
Sources
This answer is drawn from the standards and guidance below. It is general information about how these systems work — not a diagnosis of your property.