This cache is placed on the remnants of an abandoned section of the rail bridge, the rail line in question runs between the Newcastle Harbour Freight Yard and the rest of the Newcastle city/suburbs train stations.
The hint should give you a good idea of the cache hide, come from either ledge (NE side is easiest, SW side is bushier) and then walk the pipe plank, there is no need to enter the drain itself. The cache is on the first support in the image above.
Good luck and have fun!