What can go up a chimney when down but can't go down a chimney when up?

I drip from the sky with a pitter-pat song, I help flowers grow and grass nice and long.

So many types of me to choose from, you may get choice paralysis. Whichever you pick our smell is quite gruesome, and good luck pooping without butt dialysis.

What can you hold without ever touching it?

I sleep inside unfinished dreams, pressed between the printed scenes. No voice, no ink, yet still I guide, what am I that waits inside?