If you change coolant w/i 2 years you should never need to flush. Modern coolants have very good anti-corrosion packages. I would not contaminate my system w/ a flush unless I was going to totally remove flush by draining the block. This is a bitch to do on 2.5TL's and I just replace my coolant regularly.
2006 Acura TSX, 2010 Acura TSX
2005 Toyota Matrix, 1994 Honda Accord
2003 Acura MDX
I don't drive em, just fix em.