The 'tee' you're looking for is simply a standard passive 2-way signal splitter. When connected in reverse, it can act as a signal combiner. The problem most folks run into when trying this is that both antennas will receive some signal from directions other than to direction they're aimed at. When combined, the desired signal from one antenna may be aided by the other antenna... But only if the signals from each antenna arrive at or nearly in phase. If the signals are out of phase, then the net effect is a form of interference. You can try adjusting cable length on one of the lines between an antenna and the combiner... This alters the phase of all signals arriving at the combiner.
The bottom line is that it's a relatively inexpensive experiment that usually provides an unpredictable set of mixed results. Some signals will be fine while others are less reliable. Most folks end up with a spare 2-way splitter when they've given up trying to find a perfect combination of aim and coax jumper length(s).
Here's an alternate method to consider:
http://forum.tvfool.com/showthread.php?t=2882