I am presently swapping my BF 300A FEL from my B8200 onto my B8200 HST. All the sub frame has been installed but prior to the install I would like to purge the FEL of old contaminated fluid before introducing it to the HST. What is the preferred method to drain the old fluid? The B8200 HST only ever cut grass so I want the conversion to be smooth.Mark W Georgian Bay Ontario Canada