Lab Tech=Lab Manager
You are essentially responsible for keeping things running smoothly in the lab so the PI doesn't have to worry about the day to day workings. This can include making sure that the lab is up to safety and all lab chores are done. Hopefully, the lab has someone to do most of the scut work while you supervise, but you will be responsible for picking up the slack. That being said, you'll also likely have a small research project to work on as well. I'd recommend a smaller lab, because you'll have a bigger role in doing the research than a lab full of grads and post docs, where you may play more of a supportive role.
If you're planning on applying to medical school during this time, Lab tech is probably one of the best jobs you can get, because you'll have a lot more flexibility in scheduling your hours around applications/interviews than you would at any other "real world" job.