Nope.......
Thing is the drain line is in the sidewall of tank (vs sloped bottom) so there is a lip that will hold some of the stuff. Need a high volume flow to push that stuff up & over that lip.
The reason for that 'Caution' is mfg. lawyers covering their behinds......someone leaves valve closed and floods inside of rig.
I dump, then flush/rinse using OEm flush system with drain open then I close the drain valve and let the flush system flow. After about 5 mins I open drain valve and let the higher volume/level go whoosh. Then close the valve wait 30 seconds or so and shut down flush system (puts a few gallons or so of water back in tank for next time)
Then I dump grey tanks and pack up.......done
I'm not real OCD about waste tanks.......dump when full, rinse, add few gallons & call it good. They are going to get dirty again real soon.