How does the hurst line lock work? Do you press the button once to activate and a second time to deactivate or do you have to hold the button and when you release it deactivates?

 

All line locks work the same.

You can install 2 line locks for the front and rear but the most common installation is for the front brakes only.

You step on the brake. Push the line lock button and release the brake. As long as the button is held (a momentary button), the line lock holds the brake pressure for the front brakes and the rear brakes are released. You do this to do a burnout so that the rear brakes aren't dragging. It's easy to heat up the rear brakes and get brake fade.

Once you're almost done the burnout, you release the line lock. The pressure is released and the front brakes release allowing you to roll out of the water box.