Are all toilet tanks standard or can you replace the original tank mfg Gerber with another mfg American for example?

You should be able to take the old tank off and mesure the distance of the mounting bolt holes and mesure the diamiter of the water hole then go to Home Depot and mesure some of the tanks they have. I diagree with the previous answer. By the way, it's spelled: measure. Anyway, if you have a 1.6 gallon toilet tank, you should replace it with the same brand. Different manufacturers tanks will NOT work with just any toilet. If you have the old style toilet e.g. 3.5 to 5.0 gallon tank, you would have to find a junk dealer who would have the exact same type of tank.