I don't believe that this bait well pump with two exits can be used reasonable as washdown pump as she will not provide reasonable pressure due the impeller construction. A considerable strong washdown pump is a membrane pump what deliver much higher pressure and has a switch to stop the pump if pressure is hold.
Also, i am for safety reasons not at all a fan of seacock mounted pumps as they are mounted usually below water level and if they break off disaster is obvious. They are convenient to install but i consider them as dangerous after i pulled one on the Venture 34 and she disintegrated as soo i tried to unscrew her. So i installed double clamped hose with a T after the highest part of the gooseneck bend and used another pump for the live well.
I used the cheaper Seaflo pumps from Amazon on the 30ft RIB mounted in the bilge area and she hold 4 years, till when i sold the RIB a few weeks ago what is actually a longer time. I have the strongest Seaflo on a 300 gallon water tank on my truck to water the olive trees and she works well too.
I did not used it on that pump but my newly acquired 2011 Canyon had the washdown pump covered with white water resistant grease to protect motor body it from humidity and that works.
If you don't need the live well often then you can either install a Y valve to connect either the live well or the washdown pump or put a T to connect both contemporary.
Chris