OceanPro Automatic drain bung system for your boat.
Ideal for smaller tinnies and boats not fitted with bilge pumps. Simply attach the assembly inside the boats bung hole, and silicone it in. The auto drain bung will drain water from the boat when you are under way. When stopped, the rubber fins close off completely, forming a watertight seal. Also supplied are capping plugs, for extra security, so you can manually close off the valve from inside the boat. I have never used them in my tinny, as I find that no water gets past the fins at all.
The auto drain bung fits the standard larger size screw in bung holes, the outer diameter, where it fits in is 32mm. The unit is installed in pieces, and just easily clips together, once fitted, takes about 3 minutes to fit.
These are quality OceanPro products, available here for a fraction of the retail price.