I have a little specific gravity tester. If it is effective for the temp I need and not dirty fuck it.
If it isn't it gets "flushed". Quotes are because I don't use the mechanic term but a logical one. Pull the last return hose from the system so it goes down the drain, add a water source to the input so that it doesn't run dry. Run the engine until you have only water coming through. Need to make sure you have removed or bypassed your thermostat though so it actually flows. Also the technique I used to change from dexuncool to real antifreeze. No orange bullshit in my car.