From what I have found so far, White tanks are typically Polyethylene, Black Tanks are typically ABS (Not always).
And based on the texture and feel of the tank, it doesn't feel like it has that waxy/slippery feel that Poly typically has. So I believe my tank is an ABS and the fittings are either ABS or PVC.
So, I'm going to try and clean up the fittings and surfaces the best I can and apply this, which says it bonds to ABS and PVC, but not Poly. And it's more of a putty, so I can form it around the entire surface where the leak is.
http://www.jbweld.com/product/j-b-plasticweld-putty/
And if that doesn't work, I'll try this one, which is more a liquid, but says it bonds with ABS, PVC, Poly, etc..
http://www.jbweld.com/product/j-b-plastic-bonder/
Although, it may take a combination of the 2 types. (ex. Fill with the more liquid type first, then cover with the putty)