I’m actually considering getting a couple more lengths of sewer hose, connecting them up and dumping straight into the opened lid of my septic tank.
Not a problem. Good time to look down in there and inspect. Mine develops a thin crust on top so not a lot to see.
Dump the black first, when the black is empty, "walk the hose" to drain its contents into the septic tank.
(Lift the hose up off the ground an few inches starting at the MH, and walk toward the septic tank. This drains the hose.)
Then dump the gray the same way.