I have had the same issue with trimmer string looping back through some invisible opening in the sunroof and have never been able to use string to push through the full length of drain tube to clear the line. Because of this I generally pull the end of the drain line from the lower footwell of driver / passenger side and use compressed air to blow out any blockage. It seems that I have to use compressed air at least once a quarter otherwise the drivers side stops draining and I have leaks.. When trying to run trimmer string from the bottom up to sunroof I run into some sort of bind / blockage that I cannot push through. Anyone else successful in pushing trimmer string through the full length of tube? Love the LR4 except for sunroof leaks....