May I use untoiveled dishes that I have been using for a long time and do not think were ever Toiveled. And another question on the same topic: Can I Toivel new dishes in a container filled with rainwater? Thank you,

The dishes must not be used without Tevila. If you are not sure if perhaps they were toiveled, then the Bracha should not be said when they are toiveled. You may not use the rainwater collected in a container, since once it is collected in a utensil the water is rendered unfit for Tevila. The water collected in a Mikveh is done in a special way.