My AC condensate pump currently pumps through a vinyl tube directly outside my house. However, I just replaced my broken home humidifier and realized that the previous one never had its drain properly installed and it just dripped into a plastic bucket or into the crawlspace (bad). I connected the drain of the new one to the condensate pump so it can pump out the excess water from the humidifier. As it often drops below freezing here and I'm worried the tube will freeze now that the humidifier drains into the pump during the winter.

Here is the tube outlet on the side of the foundation:


I was wondering if I can tie the condensate pump line into my sewer drain in the crawlspace. I've got a shower drain with the trap in the crawlspace so I could install a PVC wye above the trap and drop the vinyl tube into there.

Here are some photos of the drain.



I assume there is a vent that goes up the wall, behind the shower and out the roof.

Is this reasonable? I was worried if I added a separate trap for the condensate pump that it might dry out during shoulder seasons when the AC/humidifier are not running. I'm not sure if this is relevant but this would become my lowest open drain and I guess would be a problem if the sewer backed up, although it seems best that this happens in the crawlspace.

I'm in Franklin County, WA if that matters, I'm not sure how to look up codes for condensate draining into the sanitary sewer.


  • 1
    If you connect a condensate drain to the sanitary sewer, it has to be through an air gap (a trapped connection might be allowed, I'd have to check the codes again). You wouldn't want the HVAC system sucking up sewer gas.
    – Tester101
    Jan 17, 2016 at 3:39
  • 1
    The pump acts as an an air gap
    – Kris
    Sep 15, 2019 at 12:32

2 Answers 2


Yes, you can plumb the outlet of the condensate pump into the tailpiece of the shower. Assuming the condensate line is properly trapped, then there should be no problem.

You'll notice in the code snippet below, that it says "If discharged into the drainage system, equipment shall drain by means of an indirect waste pipe.". Which means you cannot, plumb the condensate drain directly into an untrapped waste line or vent.

Uniform Plumbing Code

Chapter 8 Indirect Wastes

814.0 Condensate Wastes and Control.

814.1 Condensate Disposal. Condensate from air washers, air-cooling coils, fuel-burning condensing appliances, the overflow from evaporative coolers, and similar water-supplied equipment or similar air-conditioning equipment shall be collected and discharged to an approved plumbing fixture or disposal area. If discharged into the drainage system, equipment shall drain by means of an indirect waste pipe. The waste pipe shall have a slope of not less than one-eighth (1/8) inch per foot (10.4 mm / m) or 1 percent slope and shall be of approved corrosion-resistant material not smaller than the outlet size as required in Table 8-2 for air-cooling coils or condensing fuel-burning appliances, respectively. Condensate or wastewater shall not drain over a public way.

814.3 Point of Discharge. Air-conditioning condensate waste pipes shall connect indirectly to the drainage system through an airgap or airbreak to a properly trapped and vented receptors dry wells, leach pits, or the tailpiece of plumbing fixtures. Condensate waste shall not drain over a public way.

Chapter 2 Definitions

211.0 -I-

Indirect Waste Pipe - A pipe that does not connect directly with the drainage system but conveys liquid wastes by discharging into a plumbing fixture, interceptor, or receptacle that is directly connected to the drainage system.

222.0 -T-

Tailpiece - The pipe or tubing that connects the outlet of a plumbing fixture to a trap.

So you could have something like this, with the condensate pump.

Condensate drain with pump

If you can maintain the proper slope, you could remove the condensate pump.

Condensate drain without pump

In this situation the condensate pump is not required, since the tailpiece of the shower serves as the air gap. And you won't have problems with sewer gas, since the drain is protected by the trap on the shower drain.

You'll want to use proper fittings to connect to the tailpiece, rather than hacking together some leaking contraption. Without knowing the size and material of the condensate drain, I can't tell you exactly what fittings to use. In the end, you should end up with something like this.

Condensate drain tie-in

You'll cut the tailpiece, and fit in a new 45° wye. Then you'll use whatever adapters and reducers are required, to go from the condensate drain into the PVC wye. The condensate drain has to maintain the minimum slope, so you'll have to work with that as a constraint.

  • 2
    Thanks so much! Do I need an additional air gap like in an indirect waste receptor or something like this ecotech-dla.com/dla-g15.htm to prevent sewer backup going into the condensate tube?
    – s0rce
    Jan 19, 2016 at 5:13
  • It would not be code required.
    – Tester101
    Jan 19, 2016 at 10:18
  • 2
    Wouldn't directly connecting the wye to the condensate drain tube without an air gap result in any sewer back-up travelling up the drain tube instead of out. I was thinking I could do it like a washing machine drain where the tube simply hangs into the open stand pipe. Thanks!
    – s0rce
    Jan 21, 2016 at 2:07
  • 2
    @s0rce A standpipe is probably a better solution, if you're worried about a backup. It sounded like you had a specific plan in mind, so I was simply pointing out how it could be done. Without being there, it's difficult to suggest every possibility, or to evaluate which solution is best.
    – Tester101
    Jan 21, 2016 at 4:42
  • 2
    Technically, the shower tailpiece is an air gap.
    – Tester101
    Jan 21, 2016 at 4:45

As long as the A/C & Dehumidifier are above the crawlspace it's a perfectly good plan. Staple or clip the shared hose to the joist in a positive slope to the new PVC wye drain & cap the new PVC drain, then drill a snug sized hole in the cap to receive the hose to prevent slip-out.

Being a drain, without sags, freezing shouldn't be an issue. You can likely get rid of the condensate pump, now or when it dies...certainly try it. And, I commonly suggest replacing those accessible traps with a trap that has a screw-in clean-out at the bottom, it's your call.

  • The AC and humidifier are in the crawlspace. There is a pump that currently sends the water outside but I was thinking it could send it into the sewer through a trap and air gap instead.
    – s0rce
    Jan 17, 2016 at 16:02
  • Oh, I thought that was just the tube down there. Well, you have your freezing issue licked then...since the pump, usually, stays half-full. Yay, the old plan is still perfectly good to go!!! And, NOPE on the Air Gap & Separate Trap. The A/C & Dehumidifier hoses or pipes should be in very loose holes at the pump. If not, then you can just drill an intake hole or 2 in a safe spot(s), it'll act as an overflow too for when the pump dies. Stick to the plan of doing a Wye above the shower's trap, 2" up or more to avoid any impossible slosh back.
    – Iggy
    Jan 17, 2016 at 18:26
  • I've also been told that I shouldn't do this in the crawlspace and instead have the tubing from the pump go up to the laundry room and just put the tube into the same drain as the washing machine...
    – s0rce
    Jan 18, 2016 at 4:41
  • Sure, it's your place. But: Did they give you any reason? Do they think some 1/2" hose below any air flow's natural convection is going to "magically" spew methane? Did they explain an Air Gap is nothing but an empty section of the hose? Why not go super simple & just drill a nice tight hole in the cap or in the top of your ABS's inner shoulder clean-out there. You won't be violating anything & you'll be doing better than almost any pro, as you well know with the old bucket & tube through the wall highest level of professionalism hack jobs
    – Iggy
    Jan 18, 2016 at 5:14
  • The only reason I could find is the additional humidity from having the open drain pipe in the crawlspace.
    – s0rce
    Jan 19, 2016 at 5:14

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