Normally, a macro can target a specific unit. With this limitation, Misdirection macros usually require the hunter to focus a tank. TankMD adds an invisible button that updates automatically to the tank (or one of the tanks, if there are multiple).
The addon creates two hidden buttons, MisdirectTankButton and MisdirectTank2Button for the first and second tank sorted alphabetically. They can be accessed through two options.
Make a macro to click the invisible button that this addon adds:
#showtooltip Misdirection /click MisdirectTankButton
This macro can be placed on your bars and will always misdirect to a tank when the addon is enabled.
In Game Menu -> Key Bindings -> AddOns, a key binding can be assigned to "Misdirect to Tank"