All you need to do is drain it and install it, plug the extra fittings and be sure you still have a vent/rollover safety valve on the tank.
No need to wash it unless it looks nasty inside, probably just fine. A little Diesel residue or even a few cups full won't hurt anything with a full tank of gas to go with it.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-