lmorin:I was told to rinse my Apeks and Aqualung regs thoroughly in fresh after each use. That means with the "dust" cap in place so no water gets into the first stage. The second stage is self-sealing and no water gets into the critical parts of it. I have also learned through trial and error that "thoroughly" means longer than I originally thought. After each day of diving, I give do a pretty decent rinse in a shower or a tub. Upon returning home, the regs now soak in the tub for hours because I discovered that despite apparently "thorough" rinses at home, salt crystals were forming in the first stage pressure sensing cavity days and weeks after the rinse. That obviously means the rinse was not sufficiently thorough and that fresh water did not get in all the nooks and crannies to wash away residual salt. I was careful previously, but am much more careful now. Pesky stuff, that salt.
The dust cap is called the dust cap not the seal cap for a reason, the water can still enter it, its not water tight, just dust tight. I beleive at least one or two companies have created water proof ones though, I think one may be Oceanic, but otherwise dustcaps are for dust just as their name implys.