Bait tank batt - timer switch vs reverse polarity

[Dave k]

Hey guys,
Building another bait tank that will be smaller than my current one. I've got it all figured out except for one thing... I'll be running a rule 360gph pump on a 12v battery. On the fence on whether I should add a timer switch, or simply reverse the polarity of the battery to slow the flow rate. Any of you electronics experts know how much switching the polarity will slow the flow?

Thanks