Tess:
Assumption: the fact that you are "pumping" means that you are using an Auto-Siphon NOT a standard racking cane.
As a devoted Auto-Siphon user, I have 2 comments...
1) the bend is prone to cracking check there. For me, that has been the usual cause of problems. When pumping, try to push down on the centre tube not on the bent part. If this is the problem, you MAY be able to cut the bend off, and put the hose on the remaining centre tube.
2) I have never had to use a clamp to keep the hose on. For those that don't know, I ran a small Ferment on Premises for 5 years, using Auto-Siphons for racking. (That's up to 100 kits on the go at a time.) The trick (IMO) is to use hose with the correct interior diameter (id).
Finally, Tess, a standard racking cane will NOT replace the centre tube of an Auto-Siphon, as the bottom is different. Buon Vino used to sell replacement centre tubes for Fermtech. I have no idea if they still do. I have no idea what it would cost, especially with shipping. A truly EXCELLENT LHBS will sell them. I'd try to help you out, but my store closed in 2007, and YES I stocked/sold parts for the Auto-Siphon.
Steve