When following the test procedures described by USC FCCCHR for a double check valve assembly (DCVA), you are often required to use a sight tube to get the differential across the two check valves. Since each ~27.75” of water exerts 1 psi, having the gauge at an improper elevation will either decrease or increase the psid reading and introduce inaccuracy into your results. A sight (or leveling) tube will help your testing stay on the level. ST201. An articulating sight tube that can flex but stays in place when the water column is full. Comes standard with a 90° fitting and a tube just over 12”. *Patent Pending* ST201XL is the ST201 sight tube plus a removable extension tube that extends the water column of the ST201 to over 28“ that gets you to 1psi of water column. *Patent Pending*