Slow draining septic tank

[UStralian]

I've got two septic tanks, one of which only services the kitchen and basement laundry, in the configuration shown in the attached image. The kitchen sink drains directly to the septic, the washer drains to the laundry tub, which has a pump under it to lift water to the septic drain. Every time the pump turns on, the water backs all the way up to the kitchen sink, coming out the drain and the autovent under the sink.

First thought was that the tank needed pumping, but we had that done, and the problem is still there. Second thought was that the pipe out to the septic must be blocked, but I've snaked it thoroughly with a drill driven auger with a big head on it, and dropped some draino gel down there for good measure. There's a ball valve on the pump outlet to control flow, it's set as close to closed as i can make it. We can get a load of laundry done (it just gurgles a bit), but if i run the faucet straight into the tub, it backs up pretty quickly.

Any suggestions on what i should try or check next?

 

[Jadnashua]

The pump on a WM can have a pretty good volume since it's under pressure, if things can't flow properly it will take the path of least resistance.

Assuming the drain lines are properly sloped and sized, it could be that your distribution box, or worse, the leach field cannot accept a high volume and it backs up from the tank. It's more likely that there's an obstruction between the house and the tank. Smaller volumes can pass through without backing up, but the sometimes significant volume from the WM pump just fills things up faster than it can drain out.

If you have a cleanout on the line from the house to the septic tank, I'd check that first. If that's good, then I think it's more likely in the distribution box or leach field. I'm not a pro, but logic says there has to be an obstruction somewhere if it's backing up, and those are the logical choices.

Did things work okay for maybe a week or two after pumping the tank out? Or, did it stay the same? If it stayed the same after pumping, then there's something between the house and the tank. If it worked for a bit, with the tank empty, there's nothing to go to the leach field until it fills up. That moves the problem to either the distribution box or the leach field.

When stuff goes to the septic tank, it first falls into the tank. Solids fall to the bottom, then it flows out near the top - normally, the tank is full except after pumping it out. If the tank isn't cleaned regularly, more solids, make their way out, and eventually, those small particles fill in the gaps in the soil and plug up the leach field. That can get expensive since that generally means a new one. Pumping the tank regularly is lots cheaper than a new leach field.

If the water usage in the home is a lot more than the system was designed for, there's less time for any solids to fall out before things get washed into the leach field. That will lead to it failing sooner.

 

[Sponsor]

 

[James Henry]

Check the filter. It's usually at the entrance of the septic tank.