I been using the cheap end caps that should be glue into place. Which I didn't do, so the caps could be removed for easy cleaning of the tubes. This results in water leaking from the caps once the plants get larger. So this season I replace them with pressure testing caps. When you turn the wing nuts clockwise, a rubber gasket expands making a air tight seal. Turn them counter clockwise, the cap becomes loose and removeable. Lowes sell them for approx. $6.00 each.