In such a small tank just manually remove them. My preferred method is boiling water in a syringe. You can put the tip of the syringe right on the base of the pest anemone and cook it right where it sits. 10-15ml per does the job. No muss, no fuss. I have found this to work 100% of the time.
If you want to get peppermints for variety, great although you will rarely see them.