These Air Tube Diffusers are manufactured in the USA. They are designed to be a drop in system. The rubber membrane is wrapped around a hollow PVC tube. The air slots in our tubes are a little larger than other brands at 2mm long each. You get a medium size bubble which does not clog and puts very little back pressure on your system. Rated flow for the 12 inch tube is 1 cfm to 4 cfm. The rated flow for the 24 inch tube is 2 cfm to 8 cfm. The maximum flow is 7 cfm and 14 cfm respectively, for short duration. These tubes are commonly used in waste water treatment systems. Both size tubes only add an additional 12 inches of water pressure to your overall system pressure. This gives you a very low maintenance and effective aeration system. You must add small stones to the inner tube to increase the weight so it stays put on the bottom of your pond or lake. A plug is included to keep the stones in. The inlet connector is a 3/4" male pipe thread. We offer a 3/4"fpt x 5/8" barb connector so you can connect to our 5/8" sinking air hose. To clean the rubber membrane, simply wipe with a rag and clean water occasionally. USE A SINGLE 12 INCH DIFFUSER FOR HAKKO 40 OR 60 AIR PUMPS. USE A SINGLE 24 INCH DIFFUSER FOR THE HAKKO 80 TO HAKKO 120 AIR PUMPS. MULTIPLE 12 INCH DIFFUSERS CAN BE MANIFOLDED TOGETHER FOR THE HAKKO 80 TO 120.