Trub by itself won't usually clog the tube. You may have other issues. One thing to check for is icing up. Fridges are designed to move cold air from the freezer and when you make the alterations necessary for storing kegs, it can cause cold spots It doesn't have to be frozen solid, by any means...all it takes is a few ice crystals in the line to clog up.
In future, rack off the top of the trub after the yeast as settled out. You should be doing everything possible to get nothing but clear beer into your serving keg.