There's a radiator drain port under the [US] passenger headlight that should be as effective at evacuating as and less messy than pulling the lower hose. There's a block drain on the passenger side of the engine. It's like a giant brake bleed nipple that'll take a 1/2" garden hose. It should be okay to do preliminary flushes with tap water. There's a coolant overflow bottle in the passenger fender behind the wheel. Follow the hose from the reservoir that tucks in the the fender by the air cleaner. I don't know if the system can draw from the overflow bottle, but just in case, remove the wheel well liner and empty the bottle so no green coolant gets back in. No need to fill that bottle.

Pull the radiator while the system is empty to clean the core. Clean the condenser core as well. Be gentle because bent cooling fins are worse than a dirty core.

Sixto
87 300D