Which fixture is not permissible for wet venting a water closet?

In plumbing, wet venting allows multiple fixtures to share a vent pipe, simplifying the plumbing system while meeting building codes. However, not all fixtures are suitable for this type of venting due to their unique drainage and venting requirements.

A clothes washer typically has a higher flow rate and can discharge water at a much greater volume than other fixtures. This can create issues with backflow and proper venting, as it may not allow enough time for the waste to properly vent before another discharge occurs. Additionally, the clothes washer could introduce lint and other debris into the shared venting system, leading to potential clogs and complications.

In contrast, shower, tub, and sink fixtures are commonly used in wet venting configurations because they have lower discharge volumes and can effectively share the vent without causing problems with drainage or blockage. They also typically fit more neatly into the traditional configurations used in plumbing systems, making them preferable for wet venting.

Understanding the limitations of each fixture in a wet venting system is crucial for maintaining the functionality and efficiency of the overall plumbing system.