Learn English – What’s the meaning of “piss on”

I'm going to paraphrase the sentence in the way I interpret it:

They are waiting because the generation of Americans who will deliver on that boldest promise of all will not do it by coercion through violence (at the point of a gun), they will not do it with judges in the courts (with the crack of a gavel), not by passing new laws (with a speech from the well of the Senate), they will do it by gently instilling concepts into the minds of the next generation (with a book on a beanbag chair with our babies).

The language being used is very figurative and symbolic. Books, beanbag chairs, and babies collectively evoke the picture of reading aloud in a nurturing environment – something that can be done at home and in the schools.

As for the well of the Senate, other answers have explained the meaning of that phrase. I just wanted to add that I believe this comes from the physical resemblance between looking down into the round Senate chamber from above and looking down into a physical well from a similar angle.

In addition to the uses you found we also use the word "something" to describe a thing that we can't remember or don't know.

For example, "I can't exactly remember what Alice said. She said something about 'the furious five' and 'alive.'"

This is a very typical use, but not exactly like the one in the song. In the song, "something" doesn't describe the forgotten word, it stands in for the forgotten word:

"Protect the valley, something (some word I can't remember), something (some word I can't remember), something (some word I can't remember), something (some word I can't remember) alive"

This is a common* way of singing a song, or quoting a speech, that you only partially remember. It's not formal, so don't use it in an essay for school, or a published article.

*The joke here is that we might expect that a viewer of a cartoon show would sing the theme song like this, because they could only remember some of the words. We would not expect the person singing the theme song on the show itself to have forgotten the words.