Since squealer was very clever and intelligent he used his intelligence to twist the words around to make the other animals believe that it was necessary for the pigs to drink the milk.
Squeler
Squealer represents the media. Squealer continually changes his story in order to get the animals to believe what Napoleon wants them to believe. Every time the animals think that things are not right, Squealer comes to tell them a new story that explains how everything is ok. For example, when the animals see the pigs breaking the "No Animal Shall Sleep in a Bed" commandment, Squealer alters the story slightly to "No Animal Shall Sleep in a bed with sheets" making the pigs in compliance with the rules of Animal Farm.
Sex101
The pigs got the milk and apples because squealer said that since they were in charge they should get the food which gave them "brain power".
The other animals allowed the pigs to have the rights to the cows milk because they were the smartest and therefore, deserved the cows milk more than any of the other animals. Or at least that is what the pigs convinced them to think.
The pigs didn't work, not manual labor anyway. The pigs were the "thinkers" of the farm. That is how they justified getting to eat the apples and milk which Squealer said was brain food.
Squealer represents the propaganda newspaper Pravda rather than a person the way the other pigs in the novel do. The statement that Squealer can turn black into white was intended to refer to Pravda's ability to turn lies into truth. Squealer also carries the messages from Napoleon to the other pigs who simply take what Squealer says for gospel. In other words, Squealer is a method of communication from the top to the bottom with the ability to put the proper spin on the information. That was Pravda.
Napoleon has Squealer secretly paint over the Seven Commandments so that they express favor to the pigs without the other animals becoming suspicious of the pigs violating the laws.For instance, one of the original Commandments stated:"No animal shall sleep in a bed."Squealer is then employed by Napoleon to change it to:"No animal shall sleep in a bed with sheets."
the pigs got the milk and apples because squealer said that since they were in charge they should get the food which gave them "brain power"
Squealer's job was to change the commandments
Squealer calls Napoleon by the name of Leader. That can be seen in the early pages of Chapter 6. "It was also more suited to the dignity of the Leader (for of late Squealer had taken to speaking of Napoleon under the title of 'Leader') to live in a house than in a mere sty." (Animal Farm, Chapter 6) Squealer is telling all the animals that the pigs should live in the farmhouse due to the fact that they work "harder" than all the other animals on the farm.