Originally Posted by Chateau Duke To Go
Keep the valve closed so there is pressure of a full tank to move everything out when you do dump it. If you leave it open, the liquids will move out leaving the solids behind. You will develop what some forums call a "poo pyramid" in the black tank.
Not only that, but the dumping hose is not smooth and stuff will accumulate in there, making the hole smaller and smaller until it eventually backs up. If you are camping long term, figure out how many days you can go without dumping the grey and then schedule it accordingly. We can go three to four days using water indiscriminately, so I dump every three days. This is when we winter in Florida.