Yes, you can extend the normal Sanicon hose with a garden hose. Just make sure you never use it for fresh water after that. I think you can go a hundred feet or more, if it's level ground. Yes, that works for black water, since it'll all be ground up in the macerator.
The manual says:
If you wish to extend the evacuation hose, connect a 3/4 in (1.9 cm) garden hose to the end of the nozzle. Do not extend the hose beyond 150 ft. (45.72 m).
2008 King Aire 4562, Spartan K3(GT) w/ Cummins ISX, Motosat HD-SL5 w/ SWM-8, Multiswitch, HR34 Genie
2014 Jeep Grand Cherokee Overland 5.7L V8 Hemi w/ Blue Ox Aventa LX Tow Bar and baseplate, SMI Air Force One brake