96 GMC Jimmy

I have a 96 GMC Jimmy 4.3L 4x4 w/190+K miles. While turning corners I hear a water swishing noise from under the dash area. There is no indication of moisture or leaks of any kind and there is no odor like mold or antifreeze either under the dash. I looked under the right firewall area from under the car but could not locate the A/C condensation drain tube. Is this collection pan and drain tube accesable from the inside of the vehicle? How would I go about clearing out this tube otherwise? Thank you.