Don't do it
Vaginal douching (flushing the vagina for hygiene or "disinfection") is never necessary and is a very unhealthy practice.
Soap of any kind should never be used. If you think you need disinfection (e.g. discharge, odor), you need medical care to diagnose and treat it. These symptoms often are from STDs or bacterial vaginosis, and douching is especially risky if you have them. See a doctor soon.