Why can't I get a grease gun to work. It seems like a simple thing, I don't need it allot so I get the one that takes the smaller tubes, I'm on at lest my second maybe third one. They work maybe one or two times then I have a wasted tube of grease and I'm cleaning it out of the gun. The plunger just goes right to the bottom. There is no resistance when I squeeze it and they plain just don't work for me. Any ideas or tips would be appreciated. Idk me and grease guns just don't work. Please help.