If you have access to a hose then this will aid you no end, drain the radiator with the drain off valve when cold. Add a bottle of forte cooling system flush and top up with water to the cold mark. Run the engine or go for a drive to get the engine up to temp and get the flush around the whole system. Run the heater fans on full and hot settings to help get the heater matrix flushed.
Stop the motor and drain the radiator via the valve.]BEWARE THE WATER WILL BE VV HOT]
REMOVE THE RAD CAP SLOWLY and wait for the engine to cool, remove the hose from the rad to the engine on the left of the engine[ silver pipe] and more water will pour out here.
if you have a secondary coolant pump bolted to the inner wing below the header tank remove one pipe and place your hose in this hose and flush through the heater matrix untill clean water emerges. open the rad valve again and now place the hose pipe into the disconnected rad hose and back flush the rad. close the rad valve and refit the rad to engine hose and coolant pump hose and refill the header tank.
Start the engine and the header tank level will drop as the water is taken around the system so keep an eye on the level top up untill the level stays the same. drain and repeat untill you have cleared all the flush and the water comes out clear. It takes a while to flush the v6 but it is worth it in the end.