The 25366 may be purchased to replace a damaged desiccant tube. The CRS456V is shipped with this small desiccant tube attached to it. The transducer's cable includes a vent tube that terminates inside of the 25366. The desiccant tube prevents water vapor from entering the inner cavity of the transducer. The 25366 desiccant has a cobalt-free indicator that is orange and turns green when saturated. Please note: Prior to August 2019, the desiccant used in 25366 had a desiccant indicator that contained cobalt and would change color from blue to pink when saturated.