I've read alot of mixed opinions on where the best vac line is to do a seafoam job on a 2004+ with a blower. What is the proper way?

I've seen a how-to telling to use the hose in the picture below.
Also, is the middle line/hose on this part supposed to be capped off? It was capped on my car since I bought it but every other pic i've seen of engine bays has a hose running to it.