Hydraulic Line won't stay in slave cylinder
 

Ok so this is what we have, a 1992 F150 5.0L 5 speed. We changed the clutch slave cylinder and the hydraulic line that connects the slave to the master. Not a problem until we start trying to bleed the clutch. The hydraulic line keeps popping off and it won't go back in. We don't know what else to do. Any ideas??