Water pump Job

[jeeper31]

If I don't drain the coolant from the plug and just remove the hoses from the water pump and the thermostat, how much coolant will I lose?

[BoxsterSteve]

I should all come out, just a lot slower, as it will take much more time for air to get into the lines and passageways in the engine.
I opened the block drain and disconnected the hoses when I changed my water pump. I then raised the front of the car to better evacuate the radiators and front piping.
I got out 19 on the 20ish litres in the ccoling system this way.