He whines because it works.
Compare it to a child that knows if they cry you'll give them a piece of candy. You are rewarding bad behavior.
You now have to teach him he will only be rewarded for good behavior...in this case silence.
You start by teaching him the quiet command.
When he is whining tell him no, the command you choose (be quiet or no whine for example), when he stops--you might need to use the treat to distract him enough to stop whining, reward him and praise him. At first, you want to reward them pretty quickly for silence but slowly increase the time in which you make him wait until he is rewarded.
Keep practicing until he knows the command.
Then, when he whines while you are mixing his food you tell him no, the command and do not give him the food until he obeys. Same with all the other things....you don't put him down or take him out of the tub until he is quiet. He will learn only the good behavior (being quiet) gets rewarded.
It takes some time, you have to be consistent and put in the work until he understands you mean business but it can be done.