Unbolt the caliper, remove the pads and place a piece of wood between the pistons wide enough to prevent them coming out of the caliper, then gently press on the pedal until both pistons are protruding.
Give them a squirt with something like WD40 or proper brake cleaner, and a scrub with a toothbrush.
To get them back in the caliper, twist the piece of wood as far as it goes, then either use a G clamp, or some other ingeneous method using a pair of spanners. Be careful not to force them - if they don't slip in easily then you have probably twisted them.
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
