Excal 1000, Excal II, Sovereign GT, CZ-20, Tiger Shark, Tejon, GTI 1500, Surfmaster Pulse, CZ6a, DFX, AT PRO, Fisher 1235, Surf PI Pro, 1280-X, many more because I enjoy learning them. New Garrett Ca
The AT PRO is ready to go when you get it, but if you are worried about any water you can add a tiny bit of Silicone Grease to the threads of the coil plug and headphone jack O ring. It is not a true water detector and isn't designed as one, but a all around unit.
Guys I think he has the old, old AT 4, yellow Garrett, not the AT Pro. Still I am inclined to agree that if it just came back from Garetts it should be ready to go, nothing else to do.