We put Stan's sealant in all of our tubes and rarely have flats now. If the tube does not have removable core, you unscrew the nut and allow the pin to fall into the tube. Inject the Stan's, maneuver the pin back up the valve stem, replace the nut and you are good to go. If you use latex tubes you can do the same, but use a latex-based sealant like Caffe Latex.