FWIW, mine is plumbed slightly different. Waste vent runs to the aft starboard side as described, but then crosses to the port side at the transom.. The Port water vent crosses to the starboard side. So my 2 starboard vents are both the water tanks, and my 2 port vents are fuel and waste.
An issue might be that the tank is very low, and the pump out at the marina doesn't have enough lift. I struggled with that, having to fill a bucket with water, and pump that to get the pump to prime, and still struggled to get pumping started. It seemed like the vent was clogged, but I used a pressure water pump and pumped water into the holding tank though the vent, so I know it is now clear.