c# redirect (pipe) process output to another process

The much easier way would be to do just use cmd as your process.

Process test = new Process();
test.StartInfo.FileName = "cmd";
test.StartInfo.Arguments = @"/C ""echo testing | grep test""";
test.Start();

You can capture the output or whatever else you want like any normal process then. This was just a quick test I built, but it works outputting testing to the console so I would expect this would work for anything else you plan on doing with the piping. If you want the command to stay open then use /K instead of /C and the window will not close once the process finishes.