Multi colour printing without using wipe or prime towers

Most of the problems with multicolour printing revolve around the fact that when switching from one filament to another there is still some of the old filament in the system that needs to be purged before the new filament can be extruded cleanly. The usual approach is to use some sort of wipe or prime tower which is wasteful both in terms of print time and filament usage, so this is an alternative approach to the problem.