Bulkheads allow you to pass water from inside your aquarium to the outside that you can then attach standard plumbing fittings. If you want to add a sump or a closed loop water flow system, using bulkheads is pretty much required. We carry two different types, the standard ABS bulkheads that are by far the most common bulkheads, and then we offer Schedule 80 bulkheads that are heavy-duty and a little easier to install and remove. Installing the bulkheads does require you to drill a hole into your glass if you do not have one already, and we include an easy to follow chart on every bulkhead page. If you already have a hole in your tank, measure the hole and match it up with the largest bulkhead that will fit properly. If you do not have any holes in your aquarium, you can choose from any size you want to use and just follow the chart for the correct size drill bit for your tank. Clean the hole to remove any dirt, grime, or build-up that could cause the gasket not to seal properly against the glass. The bulkhead’s flange side and gasket should be placed on the wet side of the aquarium for a proper installation (putting the gasket on the outside could cause leaks.). After the bulkhead is inserted through the aquarium, you can then screw on the retaining nut, making sure the bulkhead is centered in the hole. We suggest hand tight; then a quarter turn to snug up the retaining nut. Over-tightening the bulkhead could cause damage to either the bulkhead or your tank. Once the bulkhead is installed, and any other plumbing is completed, we recommend doing a leak test. If any drips are found, more than often the bulkhead’s nut needs to be tightened another quarter turn, or there is a piece of debris between the gasket and the surface of the tank allowing water to pass through.