Engine block drain plug

It's to the left of the oil filter. Most Honda service techs don't recommend removing it though. You'll find very little comes out and its a bugger to remove and then re-torque upon replacement. May try draining the system (via radiator drain cock), take out your thermostat, fill back up with distilled water, run the car a minute, drain it. Repeat. Once it drains clear. Reinstall stat, refill with coolant, bleed the air, top off coolant. Done.