Not happy with the filthy coolant bottle, I removed it to give it a good clean. I had success in the past cleaning a coolant bottle by using soapy water and a handful of rice shaken vigorously about inside the bottle. Didn't work this case. I tried a few different things but what worked the best was Gunk engine degreaser. I gave it a good clean and then a thorough rinse. Looking much better!
But still very cloudy... I ultimately ended up replacing the bottle with a brand new one. I had another reason to replace it. The new bottle has a low coolant sensor. The car, a 2004 TF, is wired with low coolant circuit. You can see the loom plug in one of the pictures above. All it is missing is the sensor in the bottle. The low coolant light on the dash worked immediately on connecting the sensor. No other mods were needed :)