I'm not sure about what Mighty Putty would do with reaction to photo chemicals, never had to use it on my tanks...never had one that was cracked.
You're only supposed to "tap" the side not knock it. LOL
Here is a tank similar to what I have.
MINI COMPACT Adorama Mini Universal Plastic Daylight Film Developing Tank with Reel for One 35mm Film.
I used to use all stainless stell tanks and reels. Still prefer them to plastic ones but they were too expensive, and I couldn't afford to buy them when I was doing this up north.