You will hear wildly different things and certain people swearing by one media or another. My answer to your situation would be: It probably doesn't matter at all.
Let me get this out of the way first, the commercial media is usually far superior. But that is really only of essence if it is used in a commercial setting, where time is valuable. I guess you do not care if your cylinder tumbles for an hour or four hours. Virtually everything that you will use is going to work, given the right amount of time.
I have used several tumbling "media" over the years and played around with them. From commercial media, to shattered tiles, small stones, small nuts and bolts and even a bucket of beach sand.
I did find that the right amount of tumbling media makes much more of a difference than what media is being used. The right amount depends on the cylinders inner diameter and the rotational speed of the tumbler.
In the best case scenario, your tumbling media starts to travel up the wall due to the rotation. Then comes crashing from the very top of the rotation and hits the bare lower part of the wall. This impact is what cleans the walls the fastest. Now if you have to much tumbling media inside, the media that falls from the top will not hit the bare wall, but just land on more tumbling media. If you have too little media in there, it will not travel up far enough on the wall. In either case, the cleaning is sub optimal.
The exact same is true for rotational speed. If it spins too fast, the media doesn't fall from the high point, but just spins around. If it's too slow, it won't travel up far enough to fall down satisfactory.
Sand works a little different, as it doesn't really travel up far enough to fall down. It works by scrapping over the walls, which is much slower. The end result with sand is a perfect mirror like surface, very satisfying! It is of course way over top and a waste of time...
I usually start with a little less tumbling media than what I think is the right amount. It is far easier to add tumbling media than remove some. I would also suggest to throw in a around a cup of hot water with some form of mild detergent- Dish-washing soap works a treat. Once you are done with the tumbling, remove the tumbling media and wash out your cylinder with a lot of fresh water. Do your last rinse with around half a liter of very hot water. For a perfect finish, immediately flush the whole cylinder with copious amounts of compressed, preferably breathing grade, air. Steel cylinders need to be dried as quickly as possible. Cutting the end of a low pressure hose attached to a first stage works great here. A slow drying process over a "fan-like" system will always lead to flash rust. While your alcohol idea will work well, it is over top here.
Sandblasting is a great option for those with the equipment. It is however no less messy.
The problem with tumbling as well as sandblasting is always going to be the dome of the cylinder. Tumbling has little chance of cleaning the dome properly and with sandblasting you will need to manufacturer a bend nozzle.
Tumbling is all but useless for the base of the cylinder. Your best bet is metal rod with a pencil brush at the bottom to clean the bottom without sandblasting.
I always preferred a flail to clean cylinders. This is orders of magnitude quicker and usually does the job good enough. Flails also have no problem getting the dome area cleaned up. Only when the cylinder is in really bad condition would I even entertain the idea of tumbling. I use it only when absolutely necessary. Cleaning up after the tumbling process is a bitch and removing the media always messy.
Regardless of what method of cleaning you use, make sure to protect the threads. A small piece of PVC pipe works great, so do the little plastic caps that new cylinders come with.
