Dave,
1) do you have to dig out another point besides the d-box?
++ NO. The D-Box gets into all of the laterals.
2) Where does the sludge go?
It is forced out into the D-Box riser.
++ A neighboring farmer used a sump pump to send the sludge out into a nearby corn field. You could hire a Septic Plumber to pump the sludge into his pump truck.
You have REALLY a great business opportunity if no one in your area does hydro blasting septic laterals.