PondMeister Note: 85% of the orders we get for these 3” Check Valves are returned because the customer has 2” tubing. Are you SURE you have Tubing with an INSIDE DIAMETER of 3”? Hint – it is NOT the inner diameter of the “Collar” Sorry to ask but it is easier than shipping these back and forth…lol. Please verify that your tubing actually has an inner diameter of 3” If you measure the Diameter of the Walking Collar for this 3" Check Valve, it will look like this below: