We have an old Florida home with one bath. In spite of our best efforts, smells tend to linger after flushing the toilet. Could we have a hole or break in our vent pipe, and could that be the cause?

If at all possible you need to pin point when and where the odor is coming from. Does the commode gurgle when you flush it thereby letting some air to come out of it as it is being flushed?? Is it possible that you might have a shower or tub drain that you do not use?? If you do not use a drain for sometime the water in the trap will evaporate and let odors come into the house. Also can be said for any type of a floor drain, Is your washing machine in the bath room?? If so does it have a floor drain under it?? If there is one the trap needs to be kept full of water. One other possibility is that you vent is some how letting air to come back into your house from the outside.

Just because a wax seal will hold water it doesn't necessary mean that it will hold air. It's possible the wax seal has ruptured and is allowing sewer gas to enter your home every time it's flushed. Just giving you one more place to look. Good luck, Tom