you are never going to get this clean with the gravity drain method, what you need is to first remove the thermostat, and collect some bits and assortments from an auto parts store.

like a spare heater hose the prestone flush adapters that can accept a garden hose - remove a heater line and install your spare heater hose and cut it to install the adapter you bought, connect your hose to the hot side water line (washing machine line) and make sure hot water is flowing through. Open up the drains on the radiator and block

start the engine and flush it out till all you see coming out is clean water. You need a positive force behind the flush to get rid of this rusty water. Dont worry about the tiny amount of impurities in the tap water (unless you use well water) - if you are very strict on it you can blow air through the system to fully remove all water. Fill as you like.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)