Is the pump above the one you are using?
I am not sure if this will help, but there is a certain way I attach soft flexible tubing to any barbed connections.
Step 1. Boil the kettle and place hot water in a mug 1/4 full.
Step 2. Place the end of the soft hose into the boiling hot water for 10 seconds.
Step 3. Carefully slide the heated tube over the barbed fitting and let it cool. The heat softens the tube and you will find it slides very easily over the barbs and to the end of the fitting.
Be careful, the tube will be warm/hot. Grab the hose behind from where you heated it.
When the tube cools it contracts slightly and will form a very secure seal over the barb.
Then you could add a larger nylon or plastic hose clamp to secure the line.
I do not know enough about the blue drain pipe in your setup, so cannot comment on that. If it is working for you, I wouldn't change it.
For a failsafe on smaller tanks, I have seen float switches placed in the display/overflow that are connected to a switched plug that immedialtely cuts power to the return. When the level rises too much, the return is cut.
Adding valves to return pumps and restricting them can cause issues with backpressure, overheating and eventually failure, so I would not recommend it.
Rigid plumbing would be counterproductive in your situation because you would need more adaptors that what it is worth. There is nothing wrong with soft tubing at all.
I hope some of this info has helped :)
