It's good to clean it out completely after 5 uses; otherwise there is a possibility of charring rubber in areas where there may be multiple layers of rubber built up.
To clean it, heat it up and scrape it out with a scraper on a broom handle. Then start fresh with a brand new box of crackfill.
You can fill cracks as long as the pavement is 40°F or warmer. If it is colder but you need to fill cracks, use a heat lance to heat the pavement up before you apply it.
