Plastic bag works well if the conduit is partly filled with water. In this case, at 460' long, it is likely that at some point the pipe is completely submerged, unless the pipe is fairly level the entire run. If there is a low spot the pipe will fill at that point.
If that's the case, you might be able to blow some air past that point but the plastic bag may not make it past a solid slug of water any better than a mouse. Worth a try though, but next step is the rod.
Radar
