Oops forgot about Zinc and galvanic corrosion. Yes Zinc is reactive. In marine environments people add Zn rods to stop other metals of concern from reacting. Basically the Zn oxidizes more readily than the other metals and so their expensive bits are replaced as long as they add more Zn rods on occasion.
The basic reaction of corrosion is as follows:
Me(0) (solid) -> xe- + Me x+(aq)
Where a metal is oxidized and released from solid to solution. However, most metals are relatively insoluble, so the following reaction also occurs:
Me(x+)aq + xOH ->Me(OH)x (solid)
This is the precipitate that you end up seeing as "crap in the lines".
Since the above oxidation is only a half reaction, there must be some other half reaction that participates. That is indeed the case when dissimilar metals are used. This reaction is fastest when the metals are actually touching, but it can also proceed in an electrolytic medium (for example water in your loop).
I personally use the poly Ts and barbs in my systems for the most part, but because they are cheaper not due to any superiority. Avoid steel (except stainless) and Zn coated stuff and you should be fine.
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