I have never heard this, and after googling it, I see that it has very little web presence. I did find a site that said "Give that man a 20-jug salute," and another that said "Since I'm a gal with the five gallon jug salute for anything worth saluting, tonight I'll drink to tomato wine, clean clothes and good conversation." Based on those, it seems clear that the phrase means to toast something with a large quantity of alcohol. In your context, it sounds like the second person is saying, "Great, go get drunk now." Not how I would celebrate a pregnancy, pero para gustos se han hecho los colores.-I'm going to have a baby.
-Take a 5-jug salute.