Hi Kevin,
Sinking is taught to students first because it is easier to learn and practice. Once you can do it well, then you are taught Outer Dissolving because that’s a little harder to get a handle on.
If you can do both Outer Dissolving and sinking, then it’s always better to do Outer Dissolving because it’s effects are more powerful. Also, sinking is a built-in part of the Outer Dissolving process. When you scan your body from the top of the head on downward. You Outer Dissolve whatever energy you can release to gas. But whatever energy is left over (i.e. you could only take it from ice to water) you continue to sink down through your body. So the entire sinking process is part of Outer Dissolving!
As far as I know, if you can take some piece of energy to the gas stage, it’s always better then taking it to the water stage and sinking it down through your body. I’m a little suspicous of the prior sentence. I’m not sure if it’s 100% true or if there are exceptions where sometimes it’s better to sink then to Outer Dissolve. But it is my current understanding.
Hope this helps,
Janak