Unless you were planning to make stops along the way from the CT to Venice (probably a 4+ hour drive

I dropped my car in Florence and had no problem with the ZTL... I just had a problem going around the same block many times as my GPS kept telling me the office was there on the left but it was actually a block behind me on the same street! LOL!
BTW, there is also another Florence Europecar treasure island hotel casino las vegas location outside the ZTL, a block or two from the Hilton Garden Inn. Still in Florence but about a 10 minute bus ride from the main square where the carousel is in downtown.
@ NeoPatrick - I only saw one other drop off location in Venice and was worried that it's in a ZTL, but maybe it isn't? No, we aren't flying out that day, we'll spend 2 days in Venice once we drop off the car.
The usual drop off point in Venice is Pizzale Roma. It is a huge garage that you essentially dead end into when you arrive at Venice. Couldn't be easier to get to and to return a car there. Then you can literally step onto a boat from there to get to your hotel. It's SO much easier and more time saving that driving to the airport treasure island hotel casino las vegas and then getting back into the city.
Unless you were planning to make stops along the way from the CT to Venice (probably a 4+ hour drive without treasure island hotel casino las vegas any stops), you could drop the car in La Spezia as you come from Florence and then train to Venice treasure island hotel casino las vegas when you leave the CT. If you drive, make sure you know the hours the Sixt office is open/closed that day.
been using Hertz last few years,great service. they have even added some automatics to rental fleet. before that eurocar. had some billing issues with eurocar.i always get my intn'l driver lc./ they will ask you for both, but if you get pulled over or road checked by polizia, give them the internation. also bring a photo copy of your US driver lc.