Pisa is a dirty little town that I wouldn’t even bother staying a night in. The leaning tower and surround buildings are breathtaking and definitely worth seeing though. If you are staying in Florence, I would recommend making a day trip to Lucca (1 hour train from Florence) then going to Pisa (30 mins train ride south from Lucca). After that, you can take a train directly back to Florence (1hr 15mins by train).