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