I have the 15lb bottle from Harbor Freight linked above by CycleRanger, I like it. Besides holding 15lb, it is very adjustable for blast. I use the lowest settings possible to do the job. Soda lasts longer.
BIG drawback is squeezing the soda past the little opening. I'm going to have a largemouth opening welded in. But once its full, it lasts a long time.
You'll need a place outdoors to let it fly, soda everywhere. But the wind and/or rain makes quick work of cleanup. I have a large driveway pad and no neighbors. Just park the vehicles upwind and go.