So I ended up getting a new tank for my bike.  Old one started leaking gas.  What do you all recommend to clean out the new one with prior to installing it?  It appears to have some sort of preservative inside the tank.  Brown oily substance.  Would white vinegar do the trick?  Warm water with dish soap?
Thanks in advance!

By "New" - are you meaning a brand new tank from Suzuki?

If so.......I would clean out the preservative using mineral spirits.  The mineral spirits (paint thinner) must be the clear kind that is actually petroleum based - and not the new eco friendly stuff that is white colored.  Mineral spirits is a gentle solvent and will not hurt your new paint.

Put in a quart and slosh it around, then dump it out.  You can make a small plate to cover the drain hole, and use a rubber plug for the fuel inlet.  

I would not use any water based cleaning products in a new tank - you don't want to start the rusting process!