The same thing happend to the tank on my Snapper pro walk behind about 3 weeks ago. It developed a small hairline crack at the bottom where the strap is.
First, I tried normal epoxy, that lasted 24 hours then peeled off from the fuel seeping through.
Then I tried the 6 minute set JB weld, that held about a week then started leaking again and the JB weld peeled off.
About a week ago, I took the tank off again. Cleaned it really well with dish soap and water, then "plastic welded" it a little with the soldering iron, then sanded it with some sand paper, then wiped it with acetone, then put two coats of JB weld on it. So far, it's been holding. I was trying to avoid buying a $75 replacement gas tank if I could.