When it's pouring rain outside, the basement apartment of my house floods with sewer water. The basement apartment has its own front entrance and back entrance; the drain outside of each entrance, the shower drain, and a hole in the floor of the closet all back up.

It's not a simple matter of water not being able to get down the drains. Rather, sewage water rises up from the drains inside and outside the basement of the house.

There are no problems with the showers or toilets on the first, second, or third floors of the house.

(And when it's not raining, using the shower or the toilet in the basement causes the outside front drain to gurgle up with a little bit of water.)

The house was built in 1909, but I just bought the house in December, so I'm not sure how long the plumbing has been a problem.

Someone from Roto Rooter came over, dropped a snake down the sewer hole (PVC pipe that's about 5 or 6 inches in diameter and has an airtight cap on top) in the front yard, and said the stoppage isn't between the hole and the house, but rather between the hole and the city's main sewage line, and therefore the city (Washington, D.C.) must handle it.

Then someone from the city water authority came over and said the Roto Rooter person shouldn't have dropped a snake down that hole, because it's city property. But the city person didn't give an explanation for how to fix the problem.

Both people said something about a "running trap," but I read others' posts about running traps and cannot tell how important running traps are to this problem and -- if they are important -- how to deal with the problem.

Please help?

Hello sad, if the sewer is the city's property then you should call them back and explain to them that their sewer main is backing up into your basement , and that your concerned about the health hazard its creating in your home. Request that they install a backwater valve on the line going into your home, this will prevent any sewage from going into your home whenever the main backs up. Goodluck------Zeke

Zeke was bang on to advise you to install a sewer check valve, (see image)to prevent the city sewer from backing up in your home.
In my area, where we get a lot of rain, It's against the law to discharge anything into the city sewer except solids and gray water. This ban includes,
Rain water run off, AC condensate, Water softener discharge or liquid of any type.

Quote:

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Both people said something about a "running trap," but I read others' posts about running traps and cannot tell how important running traps are to this problem and -- if they are important --

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And both people were wrong! A running trap, (see image) will not prevent the sewer from backing up in your house.
Complain to the city and complain loudly. The squeaky wheel gets the grease. Good luck, Tom

I agree with Tom that both people are wrong. But then what do you expect form Wash Sanitary. Several years ago they found out that they had not billed some residents for water in about 10 years. Then wanted them to pay up all at one time. I think the Roto Rooter guy was wrong, his snake should have gone from the clean out to the city main. Therefore the blockage would be between your toilet and the clean out. If you have a PVC clean out chances are that you have PVC pipe between the clean out and the city main. Roto Rooter should have pulled the toilet and snaked to the clean out. Sound like flooding is caused by restricted drainage and rain water from stair wells. Bad idea to bring water into your house from outside but was probably done before any codes. Bad idea but it is what it is. You could install sump pumps in stair well and block drains but then you have power outages and freezing factors to condsider.