@sallyg, I don;t have fancy propagation methods LOL. I don't do water...rooting in water is a transitional step that IMHO is totally unnecessary and can actually create more problems rooting the plant than just putting it into the soil media you intend to grow it in.
If comething is specifically known to be hard to root, I will place it in moist sphagnum moss. Because that is an actual SUBSTRATE that makes the plant's new roots tougher when they have to wend their way through it to seek water. Moss rooted plants transition to soil almost seamlessly. For something like these big elephant ear tubers, its been my experience that you can cut them into PIECES and they will still root.