a basin nut wrench? Se it at; http://www.homedepot.com/p/3-8-in-x-1-1-4-in-Basin-Nut-Wrench-70236/203550156#.UitzTX_gdO8
I use one aboard and it has worked GREAT for a number of places. The end ( the black part in the photo) swivels 180 deg.
Greg