I had a couple helium tanks leftover from the kids' birthday parties, so I figured I'd take a whack at reusing them. Here's how to attach 1/4" OD tubing to one. From there, you can use it to store compressed gases (e.g. CO2, air).
Disposable helium tank (the ones I have are Balloon Time)
1/4" OD compression nut with insert
1/4" OD tubing
3/16" drill bit
5/16" drill bit
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Step 1: Cutting
Remove the nozzle. Cut the connector off as close to the thread as possible. There should be a small plastic nib inside. Remove that.
Step 2: Drilling
Drill out the valve with a 3/16" bit. A bunch of black plastic will come out. Keep drilling until it bottoms out. As far as I can tell, the plastic is a check valve that prevents refilling.
Countersink with a 5/16" bit to a depth of about 1/4".
Wrap with Teflon tape, overlapping the edge.
Step 3: Attaching the Tubing
Assemble the compression nut and attach to the connector. It just happens to be the same thread.
I've tested this up to 70 psi. Not sure how far it'll go.
I've done this with two tanks so far. On one, the valve doesn't close all the way anymore, so I put an inline valve on the tubing instead. The other one seems to work fine.
I'm currently using one for compressed CO2. Haven't decided what to do with the other yet.