Berkey Sight Glass Spigot for Royal Berkey Water Filter System. Some buildup in sight glass. Fully functional. See link below for full details. The Berkey Sight Glass Spigot provides an easy solution for viewing how much water your Berkey water filter system has left in it. Note: The Sight Glass™ is not interchangeable with other spigots and is only compatible with the spigot it is paired with. https://www.berkeyfilters.com/products/sight-glass-spigot