The tank is similar in my Mammoth. There is an external black tank flush next to the dump port. You can run water from your bathroom sink via pump if there is no water available at the dump site.
After dumping your black tank, move the hose to the gray dump and repeat. This should get most the solids out of the dump hose.
The Mammoth and Everest will weigh about the same. Expect about 4500-5000 lbs dry based on how you option it. The Cascade is a foot shorter and should be a little lighter. Mine is over 6000 lbs when loaded and filled, but my 5500 handles it without any modifications even when I add an additional 1000 lbs of trailer tongue weight.