Hook up your sewer hose and dump on site........your grey/black tanks are higher than CG in ground sewer connection.
After dumping you will have to 'walk' the sewer hose to drain it.
If the trailer leaf sprigs are mounted UNDER the axle you can do an axle flip....install the leaf springs on TOP of axle. This will raise the whole trailer and give you more clearance.
Personally......if I would just 'walk' the sewer hose
unless you really need the trailer taller for other reasons (towing level, matching to tow vehicle, off road clearance needed, clearance for different tires)