I'm not sure the usual definitions of "plumbing" apply to this context. What if I take it literally—as in straightening something out? The time frame of the Wa-rr-ing States period (Zhanguo) is not agreed upon by all historians, with some preferring 481 BCE as the starting point when the Lu chronicles end and others plumbing for 403 BCE when the three states of Han, Wei, and Zhao were officially recognised by the Zhou court.