Doug,

I'm not that familiar with the TJ system, but the system on my CJ-7 actually has two drains. There is a large drain for the intake plenum in the cowl area. This is the one that most people have been talking about. However, there is another drain for condensation and slow leaks in the heater coil. On my Jeep, that drain is just below the motor coming out of the lower part of the firewall on the passenger side. There is a metal drain tube coming out of the heater assembly under the motor and going forward through the firewall. On the engine side of the firewall, there is a short drain hose attached to the drain tube with a radiator hose clamp. That drain hose hasa 90-degreee bend in it, and the total length can't be more than 4-5 inches. If you do a lot of off-roading in mud or dusty dirt roads, that drain hose can clog up with dirt. It that drain stops up, then water will back up into the fresh air outlet under the dash and leak onto the passenger floorboard.

Hope this helps....