Depends where you are dumping at. If you are dumping where it's level not everything on the bottom will drain out. Which is why you should always (if possible) after dumping to fill with water and dump again.
If you are at a CG just raise the opposite side of your RV with levelers. Then fill with water and dump and keep filling with water and then dumping a few times. That should clean out the bottom of your tank.
We must be willing to get rid of the life we've planned,
so as to have the life that is waiting for us.
