When I drained the first time coolant went all over the floor. Why did they put the drain where you can't get to it. It is right between the trany cooler hoses. I had a problem with getting the drain plug tight. It keep dripping and I keep tighting it. As it is plastic and can strip. I had to use a need nose vise grip to get it tight. I would of just replaced the drain plug but it looks llike the catch for plug would brake off and then I would have to remove the radiator to fetch the catch. I will just pull the hose and add new coolant as I don't want to pull the plug again without replacing it. The radiator was replaced by the last owner. I replaced the theromstat and water pump last year so it should be a while before it need servicing.
If you just pull the hose off the coolant you loose will be to the height of the hose. Much better to drain the system down some first to save yourself a bath. I always replace any fluids I take out with new. I have seen recommendations for anti-freeze that say it should be changed every one or two years anyway. For the sake of 10 or 20 dollars there is a chance of introducing contaminants into the system. For those that are really into it they make filters and testers for cooling systems. NAPA sells one tester that is like Litmus paper that can be dipped into the coolant and depending on the color chemicals can be added to balance the PH etc. On some of my trucks there was a water filter in a bypass loop. After testing the coolant I could open the loop and coolant would flow through the filter which contained a chemical element for some amount of time. $.02 worth.