Capillary Action in a Bent Glass Tube

Your hummingbird feeder is of a poor design....as the air trapped in the top of the feeder is heated it will expand and force nectar out creating a drip...Here are some better designs...

http://www.wildbirdshop.com/Birding/humfeed.html

And, if the fluid level in the reservoir is higher than the end of the glass tube is now, it will siphon the water out.

I would think that filling it to a level below that would solve this problem, unless it's as SE suggests.

You' altered the differential pressure mate.

Adjust your fill height and tube insertion depth to compensate.

When you say the feeder now leaks, you don't specify the leak location. The balance of pressure inside these feeders is somewhat of a mystery. Obviously one can fill the feeder with fluid without a leak because as water leaks out, the pressure in the trapped airspace goes down, like placing the end of an open straw in liquid, sealing the end with your finger, and then withdrawing the straw. Liquid will remain in the straw until the end is unsealed. These feeders DO work. There are additional forces (such as temperature and barometric pressure changes at work. If you are experiencing leakage around one of the two seals, try using a sealant such as petroleum jelly.

I can't see that a 1/4" less of tubing length is going to change the pressure in a crude and simple system like this, to the extent that that would be the cause of it now leaking, in the way that some of you have described.

I suspect it may have more to do with the surface tension of the liquid at the lower end of the tubing having been affected by the new cut.

First of all, thanks to all who tried to help me. Bingo! The new cut was ever so slightly ragged. So it ended up...no pun intended, that the surface tension at the lower end was indeed affected by the new cut.

Bingo's are good!