Basement Drain Venting

My house is 120 years old and was originally built without indoor plumbing. Sometime in the past plumbing was added, which included a drain system in the basement floor.

I have verified that all the drains on the basement work and drain out to the same outlet outside the house.

But my question has more to do with venting.

The rest of the house drains to a stack that comes to the basement. No problem there.

There was an old bathroom in one corner of the basement. It still has the drain for the sink, the shower/bathtub, and the toilet. They drain and are not plugged up. In order to make the bathroom functional, I need to add new supply plumbing and fixtures. No problems there.

The washer drains into a floor drain near the stack, and there is a P-Trap below floor level and a cleanout. The furnace drain also drains into this drain. No problems there.

There was another open drain where a laundry sink had been. I added another sink and p-trap plumbing and that sink is draining with no problem.

There are three open drains in the floor still. There is no standing water in them and are no p-traps and they drain right into the main line going out of the house. I am thinking that it's not a bad idea to cap them to prevent sewer gases, etc from entering the house, and make a removable drain plug to drain them if the basement floods (rarely).

But my question is whether I should add some type of vent to one of the drains in the basement and vent it to the outdoors. If not, only the shower/bathtub drain would allow the drain system to vent as the others are all blocked by p-traps.

Does this make sense? Should I add a vent or allow the shower/tub to act as the vent for the system?

Thanks for reading, I hope I didn't make this too confusing!

vince

I think I have the picture. First, if you temporarily plug those drains, you will be able to see if the remaining venting will work. Second, you've been in the house for a while, any problems with sewer gas yet? And third, if your basement floods and you pop a cap off to drain it, do you know if that will allow more water in than it drains out?

Thanks S & s!

I will put a removable plug in the final one and see how it goes.

No problems with sewer gas. The basement is drafty due to old windows needing work, and sand in the center of the brick walls has shifted, etc. and between that and some crumbling mortar between bricks brings in air from outside. Funny thing is, air will flow into the empty drains as well, giving me drafty floors.

As for flooding, the septic tank has been replaced by a holding tank system that pumps waste out of the tank to a treatment facility nearby via a high pressure line. If the part of the yard where the holding tank is floods during a storm, the water will enter the holding tank. If there is an electrical problem with the system, it will not activate the high pressure pump and the basement drains will back up to the house. The basement will flood partially if the rains are exceptionally heavy. This is rare now due to drainage work in some parts of town. If I open a drain when it floods, it's hard to tell if it will flood from the drain or the outside. It depends on how the water is moving through the yard as it drains.

So I guess the only real answer is close it up and wait and see!

Thanks!