I would try flushing with plain water first, maybe a couple tank fulls.
Fill the tank, let it sit for 30 minutes or so then drain well, then repeat.
Then use a couple gallons of methanol to absorb any water left in the tank.
If you can, slosh it around by rocking the car.
Drain and blow that out well and let the tank sit open for a day or two.
The water should clean out any residual lye and the methanol any residual water. By chance if there is any residual lye it will dissolve in the methanol as well.
Once it is thoroughly dry fill it with diesel.

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Darrell

1984 300SD "Ole Girl"
207K