Insert stopper with two tubes into the 50-L LN2 filling dewar and secure using bar and 2 C-clamps.
Then screw the end of the latex tube onto the filling port on the end of the CCD dewar (9/16 wrench).
Turn on the liquid nitrogen pump from the APC power outlet web page on Chewy or Capilla (outlet #7).
You can hear the air compressor located just outside the warm room.
Beware of ice plugs in the tubes; if your fill times are longer than 10 minutes, ice is probably blocking the tubes. Watch the back end video camera (outlet #6) until you can clearly see liquid coming from the vent tube. Then turn off the LN2 pump (outlet #7, again) and uncork the nitrogen tank and disconnect it from the CCD dewar. Be careful of the pressure release. Pull the plug and tubing completely out after a couple of minutes when they are pliable. Replace the rubber stopper (one with holes for venting). Make sure nothing will block the telescope slewing motions.
Fill the CCD dewar at least 1.5 hours before dusk flats with the telescope in the stow position. Top off after dusk flast and once is needed during the night.
The hold time for the dewar is about 9.5 hours.