If you're just using Tamiya acrylics in your AB, metho is fine. Not to say Tamiya thinner is any better or worse, but metho at $3 per litre is much preferable to Tamiya thinner at $3 per 10mls.
Generally, when changing clours, I'll run water through it till it runs clean to flush it out, then run some metho through it. End of session, as above, then unscrew the head and soak it in a paint jar of metho. Wipe it down and then reassemble and it should be good to go.