It's actually "Ft", which means "Full Tank". The instruction manual says to drain the internal safety tank through the drain hoses.
To drain the tank, open the cover on the rear of the appliance.
Pull out the 2 drain hoses, take off the caps, and let all the residual water flow out.
When all the water has been drained, place the caps back on the hoses and put the hoses back inside.
It also says you need to clean the filters and let them dry thoroughly before putting them back.
This is also the procedure for "End of Season Operations."
Hope this helps!