It doesn't hurt plastic (isn't your reservoir plastic?) but it will take the paint off anything painted. But it's not like that hasn't been done a million times before. Don't lose any sleep over it.

Pacific Green '96 Contour LX V6 â??98 GTP, light mods, 14.66/94 Calypso Green '92 Mustang LX coupe, 13.56/101 Crown Autocross Club 1999 Street Tire Champion, 2000/2001/2002 Street Modified Champion KCR SCCA 2002 Solo II Street Modified Champion