This is our favorite boom pump hose setup. What you are looking at is a 5" to 4" to 3" reducer attached right at the boom so it is rigid and not swinging like a pendulum on the end of a rubber hose. We then clamp without the gasket, a piece of 4" water discharge pump hose that is about 10 long to that. The discharge hose is tight to fit on the 3" reducer, so sometimes we warm it up on the exhaust of the pump, then slip it over and clamp it. This hose allows great flexibility to the hose man and also can make a mediocre operator look darned good.