Since many are prepping their campers i thought id share this tip, I've been doing this for a while. When trying to pour bleach for sanitizing into the gravity fill I invariably put at least a quarter of it on the ground. Measuring cup, funnel, small soda (pop) bottle which still needed measuring cup and funnel were all tricky.
Then I spied my wife's gravy separator measuring cup. With the spout starting at the bottom of the cup pouring bleach became a no mess job. You can tip it enough to pour but not shoot half the contents at once to the fill hole!
-- Mark