I had this exact scenario happen to me this year and once before as well. I assume it's something to do with air being in the lines but usually turning on a tap briefly to relieve the pressure will get things moving.
Note: This time I tried to get it going by opening the kitchen sink tap with no luck. I then moved around the trailer trying other taps and when I hit the outdoor shower BINGO the suction kicked in and the pink started flowing.
2007 Shamrock F19 hybrid - 2010 (22 nights), 2011 (24 nights), 2012 (11 nights)
2013 Surveyor Select 235RKS - 2012 (6 nights), 2013 (32 nights), 2014 (26 nights), 2015 (37 nights), 2016 (14 nights)