Do you leave your dump valves open (Major mistake) Fill the tank at least 2/3 with water.. Let it sit for a day. Dump.. Do it again.,
Finally get a good tank flush wand. The "Twister" is good but not necessarily the best.. Valterra has one called "The Blaster" now that is THE best CONCEPT but again, I'm not sure it is the best design (the "Jet" nozzle looks like it might break off in use) I built my own from a 1/2 inch length of PVC a hose adapter. Vacuum breaker and end cap. I capped the end and drilled a hole just undr a quarter inch (First bit I grabbed) This can "Blast" the pyramid.
Upon remnoval wipe down with Clorox wipes