If you are referring to the 3-gallon beverage cooler, I believe that that cooler has the same valve assembly as the larger coolers. If so, all you need to do is remove the valve assembly while leaving the valve gasket in place. A bulkhead can be fashioned from a #2.5 rubber stopper and piece of 3/8 racking cane or copper tubing. The racking cane is threaded through the hole in the stopper such that about 2" is sticking out on both sides. The stopper is inserted from the inside of the cooler, small-end first, and pushed until it is tight. All you need then is a hose clamp and a length of braid on the inside and length of PVC or silicone tubing and hose clamp on the outside. I used this type of bulkhead for the better part of ten years without incident.