Wash and dry your berries thoroughly. Hull your strawberries and chop them. Remove any lingering stems on the other berries. Add to your blender container and blend until smooth, about one minute. Strain through a fine-mesh sieve into another container to remove the seeds (this is a little time-consuming, but so worth the effort!). Keep in the fridge until completely cooled (will be much quicker if you made the mint simple syrup ahead and are using that already cooled).