1. Doubt it's the flush tube it is usually the pump impelar in your case is slow intermittent movement.
These sumbersibles sometimes do jam up with lack of use in storage. I have one that does the same.
Send email to robertwhiting76athotmail.com. replace at with normal email symbol as email addresses cannot be inserted in to forum. Be quick I'm off to France in a few days. I have file on C2 Bench type
Bob
June 2009