There is this stuff -
DTG Inks - DTG Clog Protection Solution But this does not go through the print head. It only goes into the capping station. It is too thick to go through the print head I believe.
I know other people have used a special type of Windex or even Simple Green. If you do a search on Windex, you should find a post that tells you the correct one to get as the other type has some stuff that is bad for your printer. I believe Sunnydayz or Mistelwoods was the one that posted it, but I could be wrong.