Tying off the reservoir is a crucial but often forgotten step while laminating. If it is not tied it off tightly it will increase the chance of air getting into the lamination or the vacuum may pull all of the resin into the pipe without any left in the lay up and a mess in the platter. Ensure that the reservoir is tied off as soon as the resin reaches the trim lines while only leaving a small amount of resin to grind angles from. Also, be sure to leave resin above the tie off point of the reservoir; this will help to ensure that no air gets pulled into the lamination.
Some people prefer using a Yate's clamp while others prefer the "twist and tape" as shown in the video below.