Another boat question

I have been using the tub for the kicker motor for years. There seems to be a vent or something higher up the lower unit that if I just use muffs the lower gets hot??! Never a problem if I get that orifice in the water all the way. Just started using the tub on the larger one to augment that water pressure issue I mentioned. That fitting was coming apart this last time and letting too much water out….