What is the minimum required waste pipe size for a trench drain that is 8' long?

The minimum required waste pipe size for a trench drain that is 8' long is based on the capacity needed to properly handle the water flow from the drain. For an 8' trench drain, a 3" waste pipe is typically sufficient to maintain adequate drainage while minimizing the risk of clogs and ensuring efficient water flow.

A 3" pipe can accommodate a higher volume of water compared to a 2" pipe, which might be prone to overflow or slow drainage if the flow rate is significant. While a 4" pipe can handle even more flow, in most cases, especially for residential or moderate commercial applications, the 3" pipe strikes an optimal balance of capacity and practicality for this length of trench drain.

The other options would either be insufficient for greater water flow (the 2" pipe) or overly large and potentially unnecessary (the 4" pipe), leading to increased costs and installation complexity without additional benefit for a typical 8' trench.