Hi Andy,

some of the 27 have water bags - as opposed to integral tanks (i.e. wet
wings)
Look he
http://www.alexander-schleicher.de/tm/27/270_TM09_E.pdf
The 28 and the 29 seem to have integral tanks:
http://www.alexander-schleicher.de/t...graltank_E.pdf

hope this helps
Walter