How many houses have you plumbed before?

This question is asked so that the interviewer can find out what level of experience you have as a residential plumber.

If you have plumbed many residential homes in your career you could say, "I have plumbed many residential homes in my career. The most challenging time was when...." and be sure to give an insightful or entertaining example of your toughest job.

If you have not plumbed a residential home before you should answer this by discussing your most specific area of expertise.