I have a central air system with a condensate drain line that exits my home near the actual AC compressor on the side of my house. The original installers put in a cement cylinder that the line drains into, but its never been very effective at draining the water consistently (likely due to hard clay soils). This has become a stagnant water/mosquito concern and I am evaluating other options. Unfortunately I do not have a good outlet to re-route the line to - if I simply have it drain to surrounding walkways, the slope is likely to have the water draining up against the house. Likewise, I don't have any immediate planters to re-route it to without crossing walkways with pipes.

The last weekend I started digging out a larger surface in the drainage area thinking that perhaps I can re-route the drain line slightly and out of the existing cement cylinder to better facilitate drainage, having it drain into a larger surface area to improve saturation and drainage into existing soils.

I am at a bit of a loss if this is a good idea, however, and if there are any guides on how I should go about implementing this change. I believe from researching I would effectively be building out a dry well of sorts, but would like any recommendations to ensure that I can improve drainage to existing soils without posing issues later on during rainy season (I am in Southern California, so heavy rain is not very common). I would really appreciate any recommendations or guidance before I "dig myself too deep" into a hole!

Some pictures of my existing arrangement, hole I dug, and relative area around the drain line for reference. Drain Line and Existing Cement Cylinder with Poor DrainageGeneral Drainage AreaHole to Possibly Convert to Dry WellAdjacent grade sloping to house prohibiting re-routing to walkway

4 Answers 4


We see similar things like this quite often. If the pipe is not overflowing just becoming stagnant.

Get some “summit mosquito dunks” break them in 1/2 and drop a 1/2 in every month. These are fish safe and won’t hurt plants or other animals but will eliminate the mosquitoes by killing the larva.

Depending on where you live 3 or 4 tablets will last a year (not needed in the winter months). This is safer than dropping chlorine tablets in there that may harm other critters and plants.


I can't tell from your pictures if the pipe has the heat pump trap pipe or not, but my unit just drained the water on the ground. Not sure if there are regulations against that in California or not.


Copper controls mosquitoes.

Metallic copper in the water is good at controlling larva populations. I used to think it was a direct effect on the larvae but experiments showed me that is not it; they do not die. Metallic copper does markedly decrease algae growth and this is the food for the larvae.

Put some scrap copper in the cement thing you have. Cutoff piece of pipe or even a handful of pennies. That will stop algal growth and lack of food will discourage mosquitoes.


Yes the right way is to terminate the drain in Drywall,as noted by this CA inspectors pamphlet


2' square by 2' deep fill with 1" crushed stone buried 6" under the soil, 3'+ from foundation, wrapped in landscape fabric with plastic on top (under the soil). 1.5"+ pipe carries the waster underground.

That's a lot of work, if your setup isn't overflowed I'd personally just reroute the 1" pvc line to terminate above the pipe and put a screen over the pipe small enough to block mosquitoes

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