there appears to be a tank of somesort behind the gas tank in my 90 gtu that is leaking water, does anyone know what this tank is. im very new to rx7s and any help would be welcome.

 

its probably you're spare tire wheel well holder thingy, pull back the carpet on the back of the hatch to get to the spare and look.

 

spare tire well? rear wiper fluid tank? gas filler neck? sorry but theres not much back there that could be confused for a tank. if its the spare tire well then your tail lights are leaking water. you need to take them off and re-seal them with some silicone pr something rubbery.

 

Also, the drains around the hatch trim empty kinda behind the gas tank on either side.
If the "leak" is in the center then its the spare tire well.