98 Tacoma passenger floor wet

My ac evap. tank does not appear to be leaking anywhere but floor is wet on passenger side gets wet. My brother has an 02 Tacoma and his rubber evap. drain tube has a metal tube in it pointed downward, mine does not have this. On mine the rubber tube just comes straight thru the firewall and stops about 2 inches into engine compartment. Has anyone else had this problem? I have tried to clean tube with a wire and dont think it is clogged. My thinking is that going down the road vacuum builds up and does not allow the tube to drain causing evap. tank overflow. Please send any suggestions via email to kgriep@cox.net. Thanks in advance.