Just pick up your plane and rotate it. If you hear the clunk move around the tygon is still flexible. There is Tygon out there that stays flexible inside the tank for years. (Not Aerotrend) I just replumbed a 3 year old tank and the Tygon pickup was still flexible.
Not saying neoprene is bad but for me I like the slightly stiffer Tygon for not letting the clunk get stuck at the front of the tank like neoprene can or might.
No problem with the brown stopper going back into the hole either. It retained it's original shape shortly after removal.