You pressure flush the system backwards. It pushes the thermostat open and gets a lot of the junk out of the block. It also prevents scale from the block getting into the waterpump. On the Triton, this means flushing from the top hose.
I used to have an old soda/acid fire extinguisher, which I modified with a fitting for an air hose (you can also use a beer keg). It fills up with water, which you then pressurise to 120psi on top. The outlet is via a pickup which goes to the bottom of the vessel, so the pressure forces the water through. 120psi sounds like a lot, but the radiator hoses aren't connected, and you are not actually pressurising the cooling system. Basically it forces the water through at a decent speed, but low pressure. You would be surprised the amount of crap that comes out of a cooling system that looks clean. You can buy an off-the-shelf unit which does the same thing.
Unfortunately, I lent the tank out years ago, and it never came back
Now I use a fitting in the top hose that has a water and air inlet. Fill the block up, and open the air valve. Takes a few goes, but works just as well.