Peggie Hall wrote:

Then there's quality of the original tank material
itself to consider...why it split in the first place.

Thank you, someone is thinking realistically. Certainly there are good
ways to repair cracked poly, including adding a welded doubler. But
polymerized plastics do age with time & whatever their enviromental
conditions may be, and begin to lose certain properties. Unless it
were a clear case of freeze damage or a known one-incient overpressure
burst (both unlikely?), it ought to be replaced & will be much cheaper
replaced in the end.

If you must make an *interim repair* due it being the middle of an
intinerary or pending reciept & R/R of a tank, and *if* you know how to
weld poly, you can stitch it together, double it & static hydro it
in-place (suggest at least 2x the head of deck pumpout fitting).
Accept that you won't be saving any time, work or money in the end, but
adding to them.