where is the drain on the toyota 2009 highlander

Your question is pretty vague, what is this pertaining to? I'll make the assumption that you have water getting into the vehicle, so in that case, yes, a plugged condensate drain in the heater core box can cause condensate to build up and overflow into the passenger cabin. OR you can have a water channel clogged in the cowl/fender area or roofline/door area, allowing water to seep into the vehicle instead of draining to the ground.