sealing the top of a GRP potable water tank

[howlingengines]

Have an inbuilt grp tank under seats.One has a crack which I am about to fix once I have removed the tank top(screwed and sealed).
Can I use the crack sealant (Corning D781 or similar) to act as a 'gasket' for the top rim of the tank when I screw it back down again.

[tkeithlu]

You want (I think) a permanent seal for the crack and a removable sealant for the lid. Different stuff. First, stop drill the crack so it doesn't keep cracking. Seal it, the usual being 3M 5200. Then, use a food grade sealant for the lid, such as:

https://www.amazon.com/White-Food-Gr.../dp/B017MUS85E