We are building out a two-room suite that consists of a full bathroom (tub, sink, toilet) and a full laundry room (washer, sink).

There is one single door that enters into this two room suite.

I think it would be nice to have a threshold/linear drain right at that doorway ... the wainscoating of the tile in these rooms make them like a swimming pool, so the water can only escape at that doors threshold ...

So I am thinking of installing a linear drain that covers the full 32 inches of that doors threshold and draining it to daylight.

Just to clarify - this is not a drain that would see any use under normal circumstances - this is a safety drain in the event that something clogs or overflows or the supply line to the wash machine breaks, etc. - the flow of water is stopped at the threshold of the tile and does not do $50k of damage past that point, It seems like a good idea.

The only thing that nags is that the 2" drain to daylight is a heat sink / source of drafts ... so I was thinking of installing a very sensitive check valve, with a 1/2 PSI crack rating, at the end of this 2" pipe.

But now I have a check valve that might stick ... but I think I can live with that, since check valve malfunctions cause them to stick open, right ?

Is there, in fact, any problem with draining to daylight ?

Would it be better to put in a huge trap, fill it with water, and just refill it if I ever notice a draft ?


  • they use these on bathroom floor drains round here. blackwoods.com.au/pipe-tube-fittings/…
    – Jasen
    Nov 23 '19 at 1:51
  • if the trap silts up you've got a problem coming.
    – Jasen
    Nov 23 '19 at 1:52
  • Did you ever get this resolved? If so, please give a check-mark to the answer or write up your own answer explaining what you did to get it fixed and give yourself a check mark. That will help others with this kind of problem know that this has a resolution and is a good place to look for their answer.
    – FreeMan
    Aug 18 '20 at 12:45
  • The drain pipe is also a path for rodents, bugs, snakes, etc. to enter the house by.
    – Ecnerwal
    Jan 16 '21 at 2:02

I see several problems with your plan:

  • It may allow mice, insects or other critters to get inside.
  • If it's below freezing outside, the drain will get blocked with ice.
  • The check valve (even if it works properly in the first place) will very quickly get clogged with all the debris that gets washed down into the drain.

If you want to have a floor drain, then it should drain to the sewer, not to the outside. I don't know what the building code in your area says about that, but you may want to check. And you don't really need a floor drain. It's nice to have in some settings, like a commercial kitchen or a public bathroom, but it's overkill for residential.

  • 1
    Where I live, for floor drains in garages, the County does not allow floor drains to go into the septic system, they have be go to daylight instead (outside of town obviously). Nov 22 '19 at 3:56
  • @mike - no sewer here, only septic ... not in city limits. And see my comment above - this is not a drain that will (hopefully) ever get used - this is just a safety drain for malfunctions/flooding ... your point is well taken about the check valve and I think I would lean toward a big trap and just fill the trap periodically. Point also well taken about critters - I can put a screen on the end of the pipe that exits the house...
    – user227963
    Nov 22 '19 at 6:00
  • @PhilippNagel I don't think this would count as a garage, though. Nov 22 '19 at 14:11
  • 1
    @user227963, the drain not getting used much just multiplies the chance that and "check value" will end up getting stuck.
    – JPhi1618
    Nov 22 '19 at 15:23

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