Well usually if the break they break at the bend, but that's NOT what you are talking about...
I've found that people who are having issue with their A/S are usually using too large a size of plastic tubing on the end....try using a plastic hose clamp like this, over the hose somewhere along the length before the bend.
Other people have found that the gasket on the bottom end of the racking tube (that fits inside the big tube) may be bad, or dried, some have added some keglube/foodgrade silicone grease around it to make a better seal, others just put some water on top of the gasket (like with a turkey baster) inside the tube, and that makes for an air tight seal.
Hit or miss Autosiphons are hit or miss usually because of a bad seal in one of the two afore mentioned spots.