I wouldn't be satisfied with that, even though it might work.
Have him patch it with Thoro Waterplug -- that won't leak. It may need to be acid-etched after it cures, though. By the way, Lowe's and Home Depot have knock-off products that may be equal, but in my experience probably aren't.
http://www.thoroproducts.com/pdf_inf..._sellSheet.pdf
If he doesn't want to use that, get him to give you a 100% fix-it-free 2 year "no leaks, no cracks, no sags in that spot" written guarantee.
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