Standpipes for clothes washers should extend at least how many inches above the trap weir?

Standpipes for clothes washers are required to provide a proper connection to the drainage system while preventing siphoning and backflow issues. The correct answer indicates that standpipes should extend at least 18 inches above the trap weir, which is vital for ensuring that wastewater can flow freely into the drainage system and that air can enter the standpipe to equalize pressure.

This height requirement serves to minimize the likelihood of clogs, odors, and flooding, while the maximum height of 42 inches helps to standardize installations within various building codes to facilitate proper function and maintenance. The specified range aligns with plumbing standards that prioritize effective drainage and system reliability, ensuring appliances operate without compromising the integrity of the plumbing system. This setup allows for an adequate trap seal and prevents problems associated with inadequate wastewater drainage.