What does a "combination drain and vent" serve?

A "combination drain and vent" serves drain lines with horizontal branches, specifically designed to accommodate the unique requirements of a plumbing system while helping to maintain proper airflow and prevent siphoning in the drainage system.

This type of system acts both as a drain and a vent to effectively manage waste and air flow. It allows wastewater from various fixtures to flow out without creating negative pressure that could lead to trap siphonage or foul odors. The design of a combination drain and vent is particularly useful in situations with limited space, where separate drains and vents might not be feasible.

When it comes to excluding food waste grinders, this is based on the considerations that waste grinders can introduce larger solids that necessitate a dedicated drainage solution, which may not be compatible with the way combination systems typically function. Therefore, the choice highlights the importance of maintaining proper drainage and venting for multiple fixtures in a plumbing system while being mindful of certain appliances that might require different handling.