Putting End Caps on Clear Plastic Mailing Tubes can be difficult, if you do not know "the secret" to it. The end caps for our Clear Plastic Mailing Tubes are purposely made to be a very tight fit. It is not a defect. We do not want the caps popping off during the shipping process. As I show in this video, very quickly is, there is a method to applying the end cap to the Clear Plastic Mailing Tubes. As you see in the video, you cannot just put the cap on top of the tube and push down, it doesn't work. The method I like best is what I call the "Cradle" method, where you lay a portion of the tube into the cap and then "pour" the remainder of the tube into the cap. Also, these tubes are water and air tight, at the end of the video notice I very quickly press my thumb down on the tube by the end cap to break the seal and release any trapped air that may cause the end caps to "bulge".