Your washer standpipe should be vented to prevent siphoning.
I just found this forum and I hope someone can help!
short story/problem: The p trap in the basement keeps drying out
long story: we're selling our 12-year-old home, which has caused a flurry of tests and inspections in the past 10 days. Septic inspection disclosed that the pvc pipe running from the house to the septic tank had bowed, causing a slow-down in the water flow to the tank, so we dug it up and replaced a 10-foot section of pipe.
Then the water test disclosed coliform in the well water, so we chlorine-shocked the well.
As all this was happening, we began to get a strong septic smell in the basement after showering, and outside the house. The p trap from the washing machine was totally dry, so we poured water in. We poured a few gallons of water into the roof vent as well. A few days later, the trap is dry again and the smell is back.
I've also now discovered that the flexible plastic hose running from the washer into the trap was pushed way down, basically to the bottom of the trap, so I adjusted that.
You can feel air coming in through the p trap. Does the fact that you can feel air flow mean that the roof vent is not clogged? Other than a clogged roof vent, what else could cause the p trap to be sucked dry in a matter of days? Could it be the hose from the washer was too low and the trap water was sucked back into the washer? Could it be related to replacement of the bowed pvc pipe running to the septic tank? I called the septic company and she first asked something about whether the guys came inside and cleared some sort of vent in the basement when they replaced the pipe (they never went inside). Not sure what she was describing, but before we got any further we discovered the dry p trap and assumed filling it would solve the problem.
We will run a hose down the roof vent and/or snake it this weekend, but I'm not sure that it's clogged.
Thanks for any ideas.