Since the vertical flick (up close) is the most powerful attack the weapon has, try luring opponents closer (via swimming backwards) to you while managing your distance so they can’t splat you right away. This will allow you to easily take them out with a vertical flick up close.
An example of what I mean is in one of the battles I did recently in Turf War (Skip to 1:59)
RTEE-MO6T-WFY7-WC97
Any other Big Swig tips are welcome in the replies :)