George and Debi,
I have fixed my fresh water tank using a product called "Aquamend." It's a two part epoxy putty type of product. I had to create a larger hole to assure I get enough putty inside the openingtobe confidentit would hold, knowing the plastic surface alone wouldn't bond well enough. It dries very strong and seals well.
We do not use the fresh water tank to drink out of so I'm not concerned with possible contamination issues. The product is however, recommended for repair fresh water lines.
Save a few bucks and try before investing in a new tank.
I think it's a good idea to check each of your tanks for proper support as I posted a recent thread on my black tank falling through with the L-bracket twisting because oftoo much weight.
Bob and Better Half
2007 F-250 PSD, SW, CC, LB, 2WD
2006 TF32SS Cross Terrain Toy Hauler (sold)
Reese 16k slider