When pulling the plenum it is not necessary to drain all the coolant.
I only drain enough so the fluid level is below the bottom of the plenum.
I do this my removing that same hose on the passenger side and aim it downward to let it drain. Once it stops you're good to go.
I went to look for the "How to..." but unfortunately they are mostly missing
due to the move to the new webpage. I'm sure it's all still in process.
In those write-ups I documented how to do this, even in a hotel parking lot
If you'er going to remove the heads then you'll need to drain more.