Well you'd make it really easy for body removal, hopefully you'd have the dignity to ride the hearse instead of the garbage truck!
On are more serious note, it would be possible but would require a little more effort than just hopping in with a cylinder.
First of all I wouldn't use anything other than nitrogen. Sacro pods takes around 15 min until unconsciousness, so using the closest thing to regular air would be preferred since 15 min is relatively long exposure. Breathing argon for that long would give symptoms like headache, nausea, vomiting. Nitrogen is instead preferred since ordinary air all ready contains 78% nitrogen.
The amount of nitrogen needed is debatable, but quite a lot would be my answer. The suggest bin is 240 liters and the average male displaces 87 liters from a source I found, that leaves us 153 liters of air to replace with nitrogen. 2000 liters of nitrogen would be enough to fill the bin 13 times and keep a flow rate of 30/Lpm for 66 minutes. It takes roughly 15 min to lose unconsciousness and 15 min until ctb, so double the amount for a safety margin Isn't to far fetched. With 30/lpm it would take around 5 min to fill the bin with an occupant. Using more gas or higher LPM isn't really a problem, but a higher lpm is noisier and cut down the time significantly. Use big margins whatever lpm of amount of gas.
The placement of the cylinder would naturally be outside the bin, not only for comfort but to not accidentally disturb the flow of gas or doing anything else that would sabotage the attempt. Putting it outside allows us to secure the cylinder and set the correct settings before entering the bin. Securing the bin is equally important, if the bin would tip over and the occupant ejected from the bin it could be considered an epic fail. Maybe a sturdy beam/post would be a good placement, using ratchet straps to secure both the bin and the cylinder on either side.
The gas would be distributed by a nipple. Preferably at head high since there'd would be the most vacant air for gas to flow uninterrupted. Be sure to use a gasket to make an air tight seal around the nipple, to prevent any nitrogen escaping or air entering.
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To purge the existing air inside the bin I would suggest using a one way ball valve mounted on top. This would allow the nitrogen to push out the existing air inside the bin and replace it with nitrogen, It would of course also push out nitrogen and that's why the amount of gas is crucial. This valve will also benefit you with an failsafe. When the gas finally runs out and no outside air is replenished, you'd be suffocated the old fashioned way making this method even more secure. Be sure to use a gasket on this component also!
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For the final technical part of the bin is to make the lid somewhat airtight. This may be challenging since the models of bin vary, so you have to be creative. But some sort of silicon/rubber gasket around the lid is required. The gasket used for refrigerators could be used since it also requires a vacuum seal and the seal is deformable. Use a silicon binding agent or similar glue to attach it to the bin.
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To achieve a good seal, the lid has to be closed securely from the inside. I would suggest using a 90 degree hook latch. Three of them at least, one in the front and two at either side. You would have to manufacture a different hook since most of them are designed to be locked from the outside and not the inside, but this isn't a huge problem. Since the plastic on the lid isn't particularly thick, a similar sized metal bracket on the other side could be used to sandwich the plastic to strengthen the lid. As with the other components be sure to use a gasket for every hole you'd drill. With all this work we wouldn't like it jeopardized by a faulty seal, even if a small leak isn't crucial since the overpressure would hopefully stop incoming air.
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For the final touch I would consider using some form of light inside the bin, I wouldn't want to exit in complete darkness. A simple led light taped to the lid would suffice to illuminate one's final moments.
Quite a project but it's possible!