You can fit a metal water pipe over the handle of a pipe wrench. In one
nasty situation, I used two large pipe wrenches and placed 6 ft. long 2"
metal pipes over the handles of each.

The 6 ft. long pipes on the wrenches gave me a lot of leverage.

Then I had one person hold one wrench in the counter clockwise direction
while I worked the wrench on the adjoining pipe in the opposite direction.
Even with all that leverage and pounding with a hammer, it still took a lot
of force to get that old water pipe unscrewed!