Protecting tank during rebuild

I'm in the process of a major (for me anyways) rebuild on a 1982 KZ750-H3 and have pulled the fuel tank for better access to everything. I usually keep my tanks as close to full as possible to prevent rusting, but I'd like to empty this one to work on the petcock and fuel level indicator.

I'd appreciate any suggestions on what to use to protect the metal inside the tank while it's drained. I was thinking of just spraying alot of WD40 into the tank and swirling it around, dumping out the excess. Wasn't sure it this would give me any problems when I filled it again and tried to start it up.

Any other suggestions?

Thanks!

WD is the way to go...cheap and easy...when you are ready to reuse the tank, just dump in some gasoline, swirl and discard...and if a little WD remains, it won't matter...your bike will even run on this magic stuff.