Quote: Let me get this straight. The bottom hose sucks in on itself if you bring the revs up a fair bit,... or is it sucked closed in the morning when it is cold?

The bottom hose is the one on the suction side of the pump & if it sucks closed when in use it is because the coolant can't flow into the pump as quickly as the pump wants it. This will cause cavitation at higher revs, but in this case, it is a symptom, & not a problem of itself.

The coolant that flows into the pump comes from the radiator & if the pump needs more than the radiator can supply, then the radiator is likely to be in desperate need of a reverse flush, or perhaps a trip to the radiator shop for a propper cleanout.

While you are checking the radiator, pull the bottom hose & have a real good look at it. If it looks a bit suss, then replace it.