I don't think it will help much since you will not be enlarging the actual hose that goes into the tank. 1/2" vent is not large enough to get oxygen into the tank. It will allow pressure to equalize, but will not do much to aerate the tank so you do not get anerobic bacteria growing in the tank. The anerobic bacteria is the really smelly stuff. Ideally you should have 2 vents, one on each side of the tank going to both sides of the boat which will promote good flow through ventalation. That will keep smells down by promoting aerobic bacteria which does not smell. Another way to get oxygen into the tank is the Groco Sweetank system. It pumps air into the tank continously to keep anerobic bacteria at bay. I put one in a previous boat that would drive you off the dock every time the head was flushed due to the stinky air that was displaced from the holding tank. 2 hours after the Sweetank was installed the smell was completely gone and we never put chemicals in the tank again.
