I'd probably put it in a vice and drill out the start and end points of the slot. Then I'd try all the tools to find the best one for the job.
Saw this one online too: If you have a table saw, clamp a 2x4 on each side of the pipe, then use your fence to set the distance you need to get the slot cut.
Saw this one online too: If you have a table saw, clamp a 2x4 on each side of the pipe, then use your fence to set the distance you need to get the slot cut.
