help: filter flow, step up step down valving...

Hurm, check Walmart for plastic quick disconnect fittings for garden hoses. I think those are only a few bucks. You could plumb them in with double ended reducing barb fittings. Has a barb on each end of different sizes.
 
Id just like to throw out there, that those quick disconnect valves dont isolate.
meaning, once you pull them apart, there is nothing stopping the water flow.

thats why you need 2 ball valves, so water doesnt keep pouring out the other side.

also, tubing with an ID of 3/8" has a 1/2" OD .... and you should be looking around 1/2" fittings, as they are normally listed by there outside diameter, whereas threads are listed as there inside diameters.
 
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