Just wanted to confirm that if I want to use seafoam through the PVC pipe and I have an oil catch can, I would inject through hard plastic gray tube that is currently capped??
I can't see what you see, but you will have best results if you use the hose from the catch can to the throttle body. Really you want to clean the internals and not the hose and catch can. Those can be cleaned by other means, the engine can't.
You want the shortest run to your throttle body. If you have a catch can, the piping should be going from the engine to the catch can, then to the throttle. On a stock setup that is the tube you want, but you have to make sure the right side of the tube is connected to the throttle. If not, use whatever tube is. The way my car is set up, I pour it directly into the throttle since the hose goes off into space. It is how I bought the car.