Illinois Plumbing Code Practice

The correct answer is based on the requirements set forth in the Illinois Plumbing Code, which stipulates that cleanouts in horizontal drainage lines of 4 inches or less in diameter must be installed at intervals not exceeding 50 feet, including the developed length of the cleanout pipe. This regulation is important because it ensures that there are adequate access points for maintenance, cleaning, and inspection of the drainage system. Intervals that are too great can make it challenging to clear blockages or inspect lines effectively, potentially leading to more severe plumbing issues down the line. Therefore, a maximum distance of 50 feet is a practical standard that balances necessary access with efficient plumbing design.