I don't know that I'd rely on the upper fill fior adequate venting. If you fill the tank via the hose connection you could overpressurize the tank. I'd keep the lower vent. You'll need it if you ever overfill the water tank. I would simply modify it. Here's a shot of mine. It has a riser and an anti-siphon vacuum break valve to prevent draining the tank due to siphon action. there's a duckbill on the bottom to keep critters out. I fill the tank until water runs out then shut it off and no more dripping. I can carry the full 90 gallons without losing a drop.