A water lock looks kind of like this:
Mine's a slightly different design, but it works the same way.
That way, the air above the liquid is CO2, with the outside air kept out by a barrier of water. You can monitor the level of activity just by observing the rate at which it blows bubbles through the water.
The water lock normally installs in the hole through a rubber stopper you cap the container with. However, I used a small plastic plumbing fixture through a hole drilled in the top of the container, with o-rings and silicon sealant. I have two such vessels, each with a capacity of two gallons. They're cleaned and filled through a large hole that uses a cap kind of like on a peanut butter jar. Finally, there's a spout about 3/4 inch from the bottom of the container, which lets me bottle the stuff when ready without sucking out sediment. They were originally made for buying purified water out of a vending machine.
As for the OJ, what about cold-fermenting it? That is, set it up in the container with yeast and sugar, seal it, and then put the whole apparatus in the refrigerator. Seems it would lessen the chances of it fouling up, or would it be too cold for fermentation to take place?