Mine was an ABS tank, just a square plastic box with an outlet port, had to cut your own holes.
Naturally I punched a hole in the wrong place for the shower drain
Epoxy painted a piece of 1/2" plywood, RTV'd around the 'bad' hole, laid the plywood over it and screwed it down with a drywall screw in each corner, silicone caulked around the edge of the plywood and was a little more careful with the new hole ...
No leaks in 6 years.
If yours is an ABS tank, seems like the same thing, only a bigger hole.