There is a 3/8" drain line by my refrigerator. I hooked up a reverse osmosis filter to the refrigerator which drains through the 3/8" line. Lo and behold, as soon as it started draining, I discovered that water was coming out of another 3/8" drain line under my kitchen sink.

Is it okay to simply put a stopper on the 3/8" drain line under my sink and still have my filter draining through the other line?

  • Probably not ok got a photo though.
    – UNECS
    May 20, 2012 at 2:54

1 Answer 1


It sounds to me like you don't have two unconnected drain lines, you have ONE drain line that starts at the fridge and ends at the sink.

If you stopper the sink end its just going to fill up the drain line and back up into the filter.

You need to install a tie in for the 3/8" line under the sink before the trap. Do not hook it in to the main drain after the trap or you'll allow sewer gases into your filter.

  • Completely agree, It would also be helpful to know that the elevations of the two ends are.
    – pdd
    May 21, 2012 at 17:49
  • Yeah--I connected the one under the sink to the drain and the other end to the RO drain. Everything seems to be working fine.
    – Jim
    May 22, 2012 at 2:39

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