1. That's a lot of work! How can I pitch in?
2. Tom, we really need you to pitch in a little around here. There's so much work to be done.
3. We're ordering a pizza for lunch. Do you want to pitch in?
4. Tim and Sally in accounting are getting married this weekend. We're all pitching in to get them a nice wedding present.
5. We really appreciate your pitching in whenever we need an extra hand.
To pitch in means to contribute or to help.