I'm not very versed in this stuff. Recently purchased this house.

I bought an RO system from the big box hardware store. Looking at installing it. drainsetup

Directions say to drill a hole in the drainpipe and connect it to the system, only says it should be above the garbage disposal or on the other side.

Since I have another sink basin, it says I can connect the RO system there.

Problem is, the dishwasher is attached to the drain there (blue, A). I am afraid if I attach the RO system downstream of the dishwasher drain (orange, D), dirty dishwater could clog up my RO line.

In the picture, C seems to be the joint of the PVC to the drain (purple, C). Is it ok to drill a hole in there for this purpose?

Then, directions for this system say not to use teflon tape, but most of what I see online says to use it.

Finally, I am meant to attach a connector to the cold, but wonder if I could just use this part up (yellow, B).

If it just can't be done without installing new PVC drainpipes I might return it and do ultrafiltration, or something that doesn't involve drilling holes in the pipes, since I'm clueless.

Thanks all for the help!!


3 Answers 3


The garbage disposal has a dishwasher drain port (the gray hose-barbed pipe hanging out the right side of the disposal in your picture).

Move the dishwasher drain pipe to the garbage disposal, per the disposal's instructions (there's probably a plastic knockout inside the gray pipe that needs removing).

Then you can replace the existing white dishwasher drain pipe on the left side with a straight pipe, and add the RO filter drain to the new pipe.

The yellow circled part is either the diverter or an online attachment for the faucet's spray hose. Don't do anything with that.

The cold RO inlet goes at the bottom of the gray faucet pipes around the part you've circled yellow. These gray pipes for the faucet attach to your house plumbing, probably with screw-in compression fittings. There should be a screw-in compression fitting adapter in your RO kit that goes inline between the house plumbing compression fitting and the faucet's cold water pipe.

  • 1
    So what I'm hearing is, move the dishwasher to the garbage disposal, if it goes that far, and get a new pipe (part A in blue) then replace and drill into that? Commented Jan 15, 2023 at 20:43
  • 1
    @garlicoinluvr, yes, that's the plan. Commented Jan 15, 2023 at 21:59
  • @garlicoinluvr, one other thought: if the dishwasher hose is too long, you can extend it with a length of other hose and a coupler. Commented Jan 16, 2023 at 15:31

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That's (almost certainly) a dishwasher input port to the disposal. Why your dishwasher goes into the other tailpipe is anyone's guess (perhaps it came first and the disposal later?)

Either move the dishwasher output there, or use it for your RO drain.


First of all do not stress out. All the white pipes are just hand tight (no tools needed) and they are very easy to replace if you have to.

Use a bucket to catch some residue water than unscrew the dishwasher hose and move it to the top of the disposal (where a part sticks out). Go to store and buy a replacement part for that.

The cold water is connected directly to the cold water valve, not on B. To do the turn off the water valve. Disconnect the water hose. Screw in the RO part and reconnect the hose.

The drain for RO can go anywhere on the white pipe, even on the horizontal section.

  • I have a feeling the line from the dishwasher won't reach to the disposal. Commented Jan 15, 2023 at 19:31

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