Here’s the best recipe I’ve found for washing a shower curtain.
2 bath towels
1/3 cup detergent
1/3 cup bleach
1 cup vinegar
Fill washing machine with hot water and add two bath towels. Add 1/3 cup each of detergent and bleach. Run through entire cycle. Rinse in plain water to which you have added 1 cup of vinegar. Do not rinse the vinegar out. This method won’t work without the bath towels. Do not spin dry because this will cause wrinkles in some types of shower curtains. Hang to drip dry.