In theory your father-in-law is right because San Antonio plumbers often use hot air to loosen a glue joint to separate the piping. But pouring hot water down your kitchen drain once in a while will not cause plumbing problems and a need for leak detection.
San Antonio plumbers have to specifically target the joint with the hot air, concentrating on the joint for 5 to 10 minutes for 350 degrees, in order to pull apart the piping. The water temperature you use is no more than 210 degrees at it's hottest.
So not to say what your father-in-law is saying is theoretically impossible, under the right conditions with enough hot water, but it is unlikely.
Check out our Web site or call 1-800-GET-ROTO for San Antonio plumbing assistance.