Drain Restrictor is built into this 1/8 male thread x 1/4 John Guest Elbow used commonly in connections to RO membrane housings and the drain line.
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The restrictors can be difficult, if not impossible to re-use.
We recommend purchasing the elbow with a restrictor already installed.
Either this version, the John Guest version, part # 59JGFR50220, or the compression fitting version, part # 44FR125256JF.