Storing oxygen generated via water electrolysis
I think the simplest approach is to fill a test-tube with your electrolyte solution, seal the open end with your latex-glove covered thumb, then immerse the sealed end in your cell. If you can tilt your anode several degrees from the perpendicular, you should get a stream of oxygen bubbles that you can then catch with the test tube. You certainly won't get them all but it shouldn't be a problem to get 3/4 of them anyway. If you have trouble inverting the test tube without having a little air left, just slide some flexible tubing to the top and suction out the air. Take care to watch the level of your electrolyte as the solution that is displaced from your test tube will of course be filling your cell.  

After you have collected all of the oxygen you need, seal the open end of the test tube with a piece cut from a latex glove and a rubber band. You will then have a test tube filled with oxygen gas and any residual electrolyte solution.