As above. I soak second stages overnight after a dive trip. That dissolves the salt crystals that want to form in the nooks and crannies. I flush my piston regs vigorously with a squeeze bottle first, and then soak them, but separately from the second stage, which is left up on the sink counter, so water doesn't track up a hose to the inside of the first.
Then pressurize everything and blow out dry.
My sealed pistons and diaphragm first stages I just rinse off briefly.
My Atomic seconds all have the seat saver feature, which means the valve is OPEN when unpressurized. I don't worry about water getting up the hose, because the first stage is always on the sink counter when the second is soaking. After the soak, I just hang the regs through a towel ring so that the first is high and the seconds are low, and let them drip dry.
In other words, accidentally pushing the purge button is no big deal (and may get some fresh water around the poppet and orifice), as long as the first stage is higher and water can't run up the hose to the inside of the first. When you dry it, make sure to push the purge button a few times to allow any hose water to drain out.
The big deal is retained salt crystals and grit. That is what starts the chrome degrading, or the titanium to scratching the next time you pressurize the first stage. And in the second, the pressures are lower, so retained salt crystals can cause the valve mechanism to catch and stick open.
Relating all this to an Aqualung Mikron, just flush out the spring chamber of the first stage with a squeegee bottle and wipe dry. Rinse the seconds with running water in the mouthpiece and exhaust tee, and then soak. Soak the seconds separately (and lower), and don't worry about accidentally pushing the purge. Then hang them up with the first stage uppermost, pressing the purge button a few times to let any hose water drip out. Let dry. You're done.
