Would not use "any old flexible tube or funkiness", but would use a Fernco flexible repair elbow and possibly a connector sleeve. They are rubber -designed for plumbing repair(the right size)and available at Home Depot or any good plumbing supply. They use worm drive clamps to seal.
Problem will be as already stated -you need to cleanly/squarely cut out the damaged elbow and custom fit the solution either rigid or flexible. Usually have to cut back at least one side before/after the elbow to get length/alignment correct. Also, usually don't connect two flexible repair pieces together without at least a short section of pipe between them. Flexible elbows can collapse or kink under stress, too. So they must be supported.
Fernco Search @ HD