As others have mentioned, you want to leave the black tank valve closed until it is 3/4 or so full and then dump it. That give you enough liquid to create a swirling action to take the solids with it when you dump. Rather like a bathtub drain. The advantage of having full hook-ups is so you can dump right at your site at your convenience AND so you can leave the GREY tank valve open all the time. That way, you can take longer showers and use plenty water while washing dishes, etc. Normally when you are dry camping (no hook-ups) you will fill up the GREY tank days before you will ever fill the black tank.
