Wisconsin Newbie: She Didn't Land on US2 This Time

This time I rode shot gun (with a different trucker) from Michigan to Pepin, Wi and we arrived safe and without mishaps. Spent weekend learning about the small but important stuff (how does microwave work, didn't realize there was a solenoid switch on electrical panel needed to allow gas from bottle to the stove, how does the water pressure system work, where is the thru hull valve for engine water intake - in the MOST difficult place possible!!!). Engine started up beautifully and tomorrow crane arrives to hoist the mast.
Can some one comment on a back flow preventer valve that can be installed in the bilge discharge line? Size & make? Bilge pumps out and then much of water comes back in discharge tube! Due to allergies in family, I want to keep bilge as dry as possible. Tomorrow hope to adjust the prop shaft packing gland to reduce drip. Suggestions appreciated.