What you received was a small grey tube.
Notice that on one side there is a small red dot.
Insert your Midmark mouth piece into the end with the red dot (as seen in the picture). Push and Twist to insure a tight fit.
Place this union of filter and adapter into your midmark unit.
Now place the Eco Bacterial Viral filter we sent you in the other end and test.
When finished testing you can just dislodge the Eco Filter off the end of the adapter ( Leaving the Midmark Mouthpiece and adapter in the unit ) and dispose of it.
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If we can assist you in anyway don’t hesitate to give us a call