Sound words, I kinda use like a spice, here and there, peppered about. I’ll typically do them on their own line, like dialogue, because it is, in a way, dialogue. For instance, flushing a toilet, I might just put in “FLUSH!” Because, well, that’d invoke the proper image, without having to have a character announce they’re flushing, or write “The toilet was flushed”…. or the like. I mean, if a character’s in the bathroom, and a “FLUSH” occurs, you can generally guess who flushed it.