United States interface reference
Plumbing connection guide
Flexible tubing absorbs route and length variation. The thread family, tube outside diameter, gender, and sealing method still have to match exactly.
Tube sizingUse outside diameter for RO and compression tubing
Thread sealingIdentify tapered thread, gasket, O-ring, or ferrule
Drain routingKeep potable, regeneration, overflow, and DWV lines separate
US standards
Common connection families
Regional separation
Europe is not an NPT adapter variant
Record before ordering