This instructable shows how to make a container for refilling your bird feeder. This was designed specifically for long cylindrical feeders that hang vertically and fill from the top. It may work for other styles and/or applications. This design addresses the problems of:

having to carry more than enough seed out to the feeder
having to hold open a spring loaded top on the feeder while filling it
having to scoop and pour, with precision repeatedly until the feeder is full

With this thing you only need fill the BFF with the amount of seed needed, open the top of the feeder, insert the neck of the BFF in the opening, pull a string, and whoosh! I have used this for years.

Step 1: Materials

I prefer to re-use/re-purpose wherever possible:

3 qt., or so, clean, empty juice bottle. A mouth of 1" or more is important for flow of bird seed.
4" x 4" piece of inner tube or material of similar pliability
rubber cement or similar adhesive that works with the material above
2 ft. string
razor knife and/or scissors
stapler (optional)
piece of paper with a 90 degree corner (optional)

Step 2: Cut the Bottom Off the Bottle

Using the razor knife or scissors cut off the bottom of the bottle. Cut around the sides of the bottle near a ridge or indentation and leaving the ridge or indentation on the bottle for rigidity.

I prefer to start with a plunge cut with the razor and complete it with using the scissors for a cleaner and safer cut.

Take this time to remove and dispose of the label, cap, and cap ring.

Step 3: Make the Plug

If your piece of inner tube not 4" x4" make it so with the scissors. Roughly find the center of the piece of inner tube. Find where to cut out a 90 degree wedge of the inner tube such that the tip of the wedge is in the center of the piece and one side of the wedge intersects a corner of the inner tube square. I found laying the corner of a piece of paper as a template works well.

Where the sides of the wedge actually end up is not that important but following this guide does help when gluing in the next step.

Step 4: Assemble the Plug

On a dry run fold over one square corner so it meets the opposite wedge corner. You are kinda making a snow-cone type cup (upside down sloppy pyramid, upside down wide-base dunce cap, ...) with the cut inner tube. Eyeball that and get an idea of the area where the two sides overlap.

Put adhesive where the pieces overlapped. Lay the end of the string in the adhesive. Overlap the pieces like before except now there is adhesive and a string. Clamp and let dry .... and/or take the stapler and put a few staples in making sure the string is securely attached.

Step 5: Lock and Load

When the plug is complete, i.e., any glue has dried, drop the plug, point facing down, into the upside down bottle with the string leading up and over the edge of the bottle.

The inner tube works well here because it has the weight and malleability to provide a good enough seal at the bottom (neck) of the bottle on its own. Cloth may work, I did not try. Paper is too rigid I suppose.

Now fill the bottle, aka BFF, with the amount of bird seed you think you will need to fill your bird feeder. You should be pleased to find there is no seed leakage. At least once, fill the bird feeder full then empty it into the BFF, and mark the level on the BFF, to find out the most you should ever need to fill your bird feeder. You will need less for partial fills. Duh.

Step 6: Fill the Feeder

With your dominant hand carry the BFF filled with seed outside to the feeder. At the feeder open the top of the feeder with your free hand and rest the mouth of the BFF in the feeder opening. With the same hand, pull on the string and remove the plug from the BFF and appreciate the satisfying "whoosh" as the seeds rush, spill-free into the feeder. Saying "Fire in the hole" or "Incoming" as you pull the string is optional. Return to the source of the seed and throw the BFF into the bag/bucket.