snip

As you've discovered, the hose should not be cut in half, but rather at
the midpoint after installing the siphon and return pipe (or else they
would just sent you two pieces of hose ;~). I try not to have loops in
canister hoses, as it promotes air entrapment during start-up. I'm glad
I helped you find your problem, and that you can now correct it yourself.

Ok, I guess I missed something on the 'mid-point'. How do you
determine the midpoint? Do you connect both ends, then pull it
towards the filter to find this 'mid-point'... thinking about it, that
would make sense... wish I had done that when I installed the thing..