Pour 3 gallons into the empty 5 gallon jug. Do this again but only 2 gallons will fit. Now empty the 5 gallon and put the leftover 1 gallon in it. Then refill the 3 gallon again and pour all of it into the 5 gallon jug. Leaving you with 4 gallons in the 5 gallon jug. I love playing Simon Says! lol