1 For best results from your flask, before use, pre-fill for about 3 minutes, using either hot water for hot drinks or cold water for chilled drinks. 2  Never use a microwave or conventional oven to pre-heat your flask.  If your flask has not been used for some time, rinse with warm water to remove any residual odours.
2. : the degree to which something is prevalent; especially: the percentage of a population that is affected with a particular disease at a given time.
Prevalence means there is a lot of something. If you get a bad grade on a paper for having a prevalence of typos, you need to proofread your work more carefully. The word is often used to describe a phenomenon that is widespread in a community, like the prevalence of a disease across a country.