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Weird plumbing in old house - 2 sets of drains?

We have a house built in the late '20s or '30s in a place that may not have any real building codes.

Our shower, bathroom sink, and toilet all drain into the soil stack, (via a drum trap), which exits through the basement wall to the septic system.

Our kitchen sink and washer drain down through a separate drain, through a pipe running out the basement wall on the opposite side of the house from the soil stack. The kitchen/washer pipes do not appear connected to the septic pipes at all.

Our basement has three floor drains. The drain closest to the sink/washer appears to lead towards the area of the house with the soil stack (and the other two drains are closer to that side of the house).

Our gutters may drain into something connected with the floor drains, as sometimes when draining the kitchen sink or doing laundry, if we go outside, we can hear a gurgling or bubbling sound from the gutter downspout. Weird!

Sometimes after taking a shower, or doing dishes, a nasty smell comes up from the basement floor drain. Even though I wouldn't think the two (septic and kitchen/gutter) systems wouldn't be connected.

A neighbor suggested there might be a clogged "grease trap" which might account for some of the weirdness, but we have not been able to locate any such trap.

Does anybody have any idea why these things might be happening? The plumbing just seems so strange and not like what I've read about in books, even books on old houses.

Re: Weird plumbing in old house - 2 sets of drains?

You have a grey water system along with the septic system. The grey water from laundry and dishwashing often has more chemicals including bleach that interfere with the septic system so they just dump the grey water into a hole in the ground.

Re: Weird plumbing in old house - 2 sets of drains?

Yes a grey water system.

After years of neglect, the grey water system has managed to collect some "organic material " Especially if there is a garbage disposal in the kitchen, or a dishwasher (which has a built in garbage disposal in the more modern units)

Time to connect everything to the black system and seal off the grey, or clean out the grey system, or make a new grey system if your local authority allows it.

If you do have a garbage disposal or a dishwasher, that will need to be plumbed to the black system.

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