Here are a few places where you can hang out with locals and try a fun Venetian tradition. All are located near the Rialto vaporetto stop.
Osteria alla Botte
5482 Calle della Bissa (east end of the Rialto Bridge near Campo San Bartolomeo)
Closed Thu. and Sun.
Osteria Sora al Ponte
1588 Ponte delle Beccarie (near the Rialto Bridge Market off of Campo de la Beccarie)
122 Campo San Giacometto (west end of Rialto Bridge along the Grand Canal)
Closed Sun. (dinner) and Mon.
For more on dining in Venice, check out Eating & Drinking in Italy: Italian Menu Reader and Restaurant Guide.