Polyethylene Water tank repair kit

[jhortonvt]

I need to cut a hole in the top of my 11 gal Plastic fresh water tank to reach in and clean algae stains. I’ve done two treatments of bleach solution, and although the algae is likely dead, it looks like I need to mechanically remove it.

So afterwards I'll need to patch back in the cutout, and I was wondering if anyone had any experience with Marine-Tex Poly-Dura:

http://www.*******.com/shop3/store/viewItem.asp?idProduct=13512

(That's boat fix dot com, why did it do that?)

Or if anyone recommends something different.

Thanks in advance