This is not valid C/C++ (you need a type specifier):
TankThermometer = { 0x28, 0x2A, 0x3A, 0x59, 0x04, 0x00, 0x00, 0x8B };
OP's first post had:
DeviceAddress TankThermometer = { 0x28, 0x2A, 0x3A, 0x59, 0x04, 0x00, 0x00, 0x8B };
DeviceAddress is declared in DallasTemperature.h:
typedef uint8_t DeviceAddress[8];
This, for example, is allowed inside a function. The definition need not be global.
char TankThermometer[] = { 0x28, 0x2A, 0x3A, 0x59, 0x04, 0x00, 0x00, 0x8B };
Just so it's understood, even inside a function, this is an initialization, not an assignment.