Smoke test to find drywell outlet??

The plans of my house say there's a 500gal drywell somewhere (ambiguous) in the backyard where the dedicated washing machine drain goes to from within my below-grade basement. I live on a hill, and have never seen water coming out anywhere in the backyard or (during a dry summer) anything greener than other spots. Yet, on cold days I can feel cold air coming up from this drain pipe (there's no trap on the line), and in summer I sometimes smell the mildew smell from out of the pipe. Where can I get a plumber's smoke bomb (?) to do a smoke test and see if there's an outlet to open air for it? I figure I'll tie it to a wire, light up the bomb, hold it down the pipe, and force the smoke "down" into the drain with my leaf blower.
It's not just for curiosity; I plan on doing some backyard regrading and want to know if there's a hidden discharge pipe (sitting under a rock) that I should avoid damaging.
Recommendations appreciated. Thanks Theodore
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I'd check with either farm and garden places. They might have "woodchuck bombs".
Or a bee supply place. Bee keepers often use smoke devices to move the bees away from a hive, so they can harvest the honey.
Some heating and AC supply places have smoke bombs for testing ducts.
Christopher A. Young Learn more about Jesus www.lds.org .
The plans of my house say there's a 500gal drywell somewhere (ambiguous) in the backyard where the dedicated washing machine drain goes to from within my below-grade basement. I live on a hill, and have never seen water coming out anywhere in the backyard or (during a dry summer) anything greener than other spots. Yet, on cold days I can feel cold air coming up from this drain pipe (there's no trap on the line), and in summer I sometimes smell the mildew smell from out of the pipe. Where can I get a plumber's smoke bomb (?) to do a smoke test and see if there's an outlet to open air for it? I figure I'll tie it to a wire, light up the bomb, hold it down the pipe, and force the smoke "down" into the drain with my leaf blower.
It's not just for curiosity; I plan on doing some backyard regrading and want to know if there's a hidden discharge pipe (sitting under a rock) that I should avoid damaging.
Recommendations appreciated. Thanks Theodore
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It should have a trap and vent.
and in summer I sometimes smell the mildew smell from out

Why would you expect an outlet if it's a drywell? The drywell's I've seen have not had any opening.
I figure I'll

Then evacuae the house..... I doubt you're going to force enough smoke down the pipe to accomplish anything.

I'd be more worried about hitting the drywell itself or having a pickup truck fall into one. Even if you hit the pipe, what's the big deal? It can be easily fixed. I would just treat the suspect area more carefully.
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wrote:

My neighbor has a drywell under a bush. It has a manhole sized (and weight!) slotted cover over it, so it has an "opening".
I installed a drywell outside my basement door since it is lower than the backyard. Torrential rainstorms would fill the below-grade 4' x 4' walkout area. If it filled with more than 3" of water, it would come in under the door. I buried a 55 gallon plastic drum and built a removable "deck platform" over it. It would now take at least 55 gallons plus 4 ' x 4 ' x 3" of water before it would come in the house. In the 20 years since I installed the drywall we've never had a problem.
The point of all that is that the drywell is open at the top (and bottom) so it does indeed have an opening.

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On Sat, 28 Apr 2012 00:03:30 -0700 (PDT), millinghill

If it's a straight pipe, you could take some thin pipe and screw sections together and keep pushing them in until they stop. That will tell you how far out in the yard it is, and you'll have to judge whether it's straight out or on an angle. If it's made of metal, a metal detector may help too. Once you have a basic idea of it's location, just bang on the ground, and use a piece of hose. Place one end of the hose to your ear, the other end to the ground. Have a friend bang on the ground and listen for a hollow spot.
As far as the odor and cold air, I'd place a fernco coupling from your inlet (wash machine) pipe or hose to the drain pipe. They do make ferncos that reduce size. However, I wonder if a vent is needed to make it work. Since there is no visible outlet there might need to be a vent. In that case, add a trap.
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You could try placing a speaker directly on the opening, play music, listen outside. I once checked roof drains like this.
Greg
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