1)
What counsel did he seek?
1.
Malbim: After he gave a bribe to Melech Ashur, he took counsel how to cast off his yoke. The counsel was to stop the springs, so soldiers besieging a city would not have water to drink.
2)
Why does it say (Pesachim 56a) that Chachamim disapproved that he closed the river? He consulted with "Sarav", which includes Chachmei Yisrael ? "Sarei Alafim" (Shemos 17:14) are the Chachamim and Shoftim!
