Can I connect a toilet to what we call in Australia to a gully trap? Of course I'd have to seal the top of it and provide a vent pipe... I just want to know if it is feasible

Are you talking about one of these? http://econtent.tauranga.govt.nz/data/water/files/waterline_gully_traps.pdf

With some modification, you could connect toilet to gully trap.

Milo