I cleaned and reused the first tank that had menthol. I tried to blow out the old juice from the atty. It took about 1/3 of a new tank to get rid of the menthol taste (the tank has clove in it now). The flavor of the clove is a bit uninspiring, but it is DIY so that could be my fault. I am not sure what to do about the residue of taste left over from the previous flavor.
Filling the tank was easy, but my method is a little messy (and probably will be until I get the hang of it). I put the tank hole to the dripper of my bottle then turned them so the bottle was upside down and squeezed. A small amount of juice ended up outside the tank. I don't have the patience to use syringes because it would have been more work to clean a syringe out than it was to just put my finger over the hole of the tank and rinse the excess juice off real quick. Both methods involve a small amount of waste (like the small amount you just can't get out of a syringe and needle).
Some juices are harder to get out of an atty (even ones that are not for the ego-t) and usually have to be either vaped out of there. Some use flavorless juice to accomplish that purpose. The other option would be to clean it out, which would be the advantage of having extra atties.