Refer to the FAQ for more information. Yes, you can flush the entire cooling system with a garden hose, and if you've never done it it might be a good idea to do a thorough job now.

Basically you just drain the cooling system via the drain tap (passenger side, bottom of block) and the bottom hose nozzle of teh radiator (messy, but there isn't a better way to get the dregs from the radiator).

Once finished draining pull the thermostat housing off and shoot water from a hose through the head/block (via opening) to drain out the tap. Run it until the water coming out the bottom is near clear. To clean the radiator just do the same thing, shooting water in the hose openings to wash the insides. I would also recommend giving this treatment to the expansion tank as well.

Have a big pail to hold all the drained and washed out coolant, and find out where you need to take it (reclamation center) since the stuff is nasty and must be disposed of properly (get some 5 gallon buckets at home depot).

Once you are finished let it drip dry, close the drain tap, reconnect all the hoses, and fill it up with a 50/50 solution. Note that there is sometimes an issue with air pockets in the head refusing to heat the thermostat (no liquid if it doesn't fill). I usually fill the head at the thermostat opening to make sure its full, close it up, and then fill the rest of the system.

Once full run the car to operating temp, make sure it doesn't overheat, turn off the car and top off the expansion tank.

All done.

-rt