I received this great tip from master gardener, Marta Waddell.
First get the jars you wish to use and wash them and then sterilize by boiling for 10 minutes submerged in the boiling water. I use 1/2 gallon (2 quart) jars for grapefruit, quart jars for orange, and half pint for lemon juice. Put the flat lids in a saucepan of hot, but not boiling water on the stove.
Juice your citrus fruit and strain out the pulp if desired. Add sugar only if desired. Place in a large stockpot and bring to nearly boiling (190 degrees F) for about five minutes. In your boiling water canner or large stockpot with trivit or rack on the bottom, fill half full of water and bring to the boil. Fill a hot jar with juice, wipe rim, top with lid and seal with band. Place filled jar into boiling water and repeat until all jars are full and in the canner. Jars must be covered by one to two inches of water. If there is not enough, add more BOILING water to the pot. Return the water to a full rolling boil and begin your timer.
Process for fifteen minutes for one-quart or smaller size jars and twenty minutes for half-gallon jars. When finished, turn off burner and let water stop boiling. Remove jars and place on a towel away from draft. Place jars at least two inches apart. Allow to cool to room temperature. When cool, test the lids for a sealed vacuum, label with contents and date, and store. Any jars which did not seal can be place in the refrigerator and used within about 4-7 days.