I wanted to be able to apply drywall compound from a caulk tube to do some touch ups on one of my projects. Nobody seems to make drywall compound or spackle in a caulk tube. Empty caulk tubes are also not readily available. None of my local hardware stores carry them. I found a few suppliers selling them online, but they were pretty expensive with shipping factored in.
The only supplies you will need are:
A caulk tube (preferably with water based contents)
An air compressor with an air nozzle
Optional: bottle washer attachment for faucet
Step 1: Empty the Caulk Tube
If you just want an empty tube to use, but don't have a spent one from a project, you can buy a new tube of painters caulk for $1.38 at Home Depot. Obviously, it is least wasteful to use the caulk for something rather than just throwing it out. But, if you don't need the caulking and need the caulk tube, this is the cheapest way to go. Buying empty tubes online and having them shipped will run you at least $3/tube.
Step 2: Extract the Caulk Plunger
I also tried using a steel rod to push the plunger out, but the rod poked through the plunger.
If you don't have an air compressor, you might try one of those cans of compressed air. I haven't tried that so I don't know if it will work.
Step 3: Clean Out the Caulk Tube
If the contents of the tube are not water based, you will have to use the appropriate solvent to clean it out. This is probably not worth the trouble or expense, so I would stick to recycling caulk tubes with water based contents. You might be able to use a rag and a paint stirrer to clean most of the residue out also.