Unlike a standard 32/40mm waste pipe from a sink, a soil pipe is typically 100-110mm (4 inches) in diameter. It connects WCs, bidets, and sometimes soil stacks to the main drainage system. Blockages here are critical because they handle solids and paper.
For a truly deep understanding, study (drain and sewer systems outside buildings) and Building Regulations Part H (UK) or IPC/UPC (US) – these detail minimum pipe slopes, access intervals, and design flow rates that prevent blockages from occurring in properly designed systems. unblocking soil pipes