I was able to get the G/Flex 655 we will see if it works.
West Systems does not post drinking water safety info. Generally epoxies are fine if properly mixed and many are certified for drinking water. You could always overcoat it with something certified (Sika 291 is certified, for example).
I'd lay some finish glass cloth in with the G-flex if I was you. I've done it that way. Also, you will notice that flame treating is very important. BTW, this does not work with most epoxies, at all.
(Last number is bond in PSI--this agrees with my testing.)
Polyethylene (HDPE) 655 80-grit sand 400
Polyethylene (HDPE) 655 80-grit sand, flame treat 1890
Polyethylene (HDPE) 655 Alcohol wipe, flame treat 2312