The 'feminising' soaks and treatments on the market are snake oil. I've tried one- Sensa Soak- what a crock.
If 'feminized' is REALLY important to you, go with fem seeds... otherwise, try the things that PROMOTE females, such as blue light very early in the seedling stage. Try out the 'Ott Light' as a good cheap source of blue spectrum light to supplement your regular flouros during the seedling stage.