Washer water goes in to black tank.

As with many of these posts (and as noted in the stickies on how to post) we really need to know the make, model and year of your rig. Consider spending a few minutes creating a signature with that info in it.

Ours goes straight out, no tanks involved. Make sure the drain cap is off and the stinky slinky attached. You could be back-filling the black tank through a leaky gate valve.