Take another look at the original sentence:
You wanted to fix it this way:
A comma splice contains two complete sentences incorrectly joined with a comma. Richard squeezed, thumped, and shook the empty shampoo bottle ... begins the first sentence. Since the bottle was completely empty, Richard worked up a lather ... starts the second sentence. Just because you add the transition consequently between these two parts doesn't alter the fact that you still have two complete sentences joined with just a comma.
You might want to consult the rules for fixing comma splices and fused sentences.