An inner flange to assist with joining the two halves of the sump tank was constructed by making a plywood sheet with a cutout slightly smaller than the opening in the tank. The inner surface of the plywood was covered with duct tape for release. Working inside the lip of the plywood, 2x BID was laid up inside the tank edge and onto the plywood.
I let this cure a couple of days before trying to remove the plywood sheet.
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