Help, fresh water won't fill all the way

I use a piece of hose ( 3 foot white fill hose with female end still on) that I attach to my garden hose that is small in diameter then the fill connection and that got rid of my problem, turns out I was putting in more water then my vent would vent. Have you tried filling it slowly.

My vent is a 1/4" fitting with same size hose on it and was using a 5/8 garden hose that sealed off (almost) when shoved in the fill, so using a hose that was smaller allowed air to vent out at the same time.