Sfax is a city in Tunisia.
North towards Tunis
Before the high way there are 3 petrol stations in which you can get a ride to Tunis (OiLibya, Shell, TOTAL. To get there from city center, you can get a shared taxi from here and a bus from this station.
Places to avoid
Accommodation and Sleep
Other useful info
There is active facebook groups for carpooling from and to Sfax:
Mostly it's in French, but you can post in English. The ride to/from Tunis costs 15 TND ($5) per person.