Howdy folks we just picked up a new to us silverlite living quarters trailer. My question is this two things one were does the shower drain at? Does it drain into the black water tank? Or the gray like every other rv? My showers backed up after only taking two showers and at the moment cannot drain the black. I've drain the gray tank and nothing changed, is there a valve I'm missing??? I've plunged it and it feels solid like it's full. Second under the sink there is a three way switch and no mechanic can figure it out any ideas factory or not?