Put Plums and Cider Vinegar in sc. I used a 6 litre sc.
Cook on low for 3 hours.
Add water.
Cook on low for another 3 hours.
Turn off slow cooker and leave overnight.
Then strain liquid through muslin lined sieve into a large saucepan. Add ginger and star anise and sugar. (1 cup of sugar for each cup of liquid.).
Bring to a simmer and simmer 15 minutes.
Bottle in sterilised bottles.