I bought one of those tonight. They had them on sale at O'Reilly for $5 off. The first thing I did was fill it up with water at the kitchen sink to see if it would hold water like it's supposed to. I holds the water in as long as you don't fill the water ABOVE the filter. Go above the filter and the water will leak past the filter cap and go down through the center of the filter. Why they don't have the top of the filter sealed I don't know. But anyway, it works as it's intended to. It has a little reservoir below the filter for the water to collect in as you're pouring the gasoline through the funnel. Oh by the way, it's made in USA by the FloTool people.
Mr Funnel
Mr Funnel