We have an issue with the city's sewer system in which when it rains (pours, hard) water will come back into the house from out back. The clean out "flap" will close outside but it's never air tight, thus allowing some water back in. the only place it comes in is under our toilet in the basement... is there some sort of trap or hinge to put over the flange... almost like the toilets in rv's that won't permit water to come up, only go down? Thanks in advance.

You need to talk to the city sewer department before you attempt repairs. Storm water and sewer should be in separate sewer lines. Storm related flooding is generally caused by the storm sewer backing up into your floor drains not the toilet.

Well it comes to the floor drains also, we only have 1 for our hot water heater, it never over-flows there though, only under the toilet... our sump cuts on and off but for some reason it still comes out under the toilet... the city usually comes out and "cleans out" the sewer (according to them, they've been out 4 times in the last 5 months)... my theory is that if I can get it to stop coming in under the toilet that it will be forced down to the sump pump

The toilet and the sump pump do not go to the same drain pipes, or at least they should not. When the city cleans the drains they apparently are not doing a great job. Silt and sediment as well as sewage slow build up in the bottom half of the pipe and they just aren't getting it cleaned out properly. Your next call should be to the Superintendent of the Sewer Dept.

This is essentially how my basement is set-up (sorry, quickie paint job)
Attachment 2747

I will attempt to get this fixed with city utilities tomorrow, but in case the problem arises again... is there a way for me to prevent the water from backing up under the toilet?

You could install a backwater valve on the main line after it exits the building.

The main line is buried 8 feet and has a cleanout installed already, unfortunately the flap on the cleanout won't stay air-tight when water is pushing against it

Ummm...

I didn't recommend you install a clean out, I recommended you install a back water valve.

Huge difference.

Growler got it. The backwater valve also must be accessible for maintanance

Perhaps you house is properly plumbed with the sump pump and floor drain connected to the storm sewer and the toilet to the sanitary sewer. Or maybe vice versa. Legal or not, your toilet is clearly connected to the storm sewers. That doesn't mean there aren't other storm water drains tied into the sanitary sewer backing up into your toilet when it rains. Combined sewers are a big problem in some places, here for instance. Fixing them is going to cost jillions.

So what do you need for an accessible back water valve, and 8' deep man hole?

If water incoming out between the floor and toilet, the wax ring is bad. If you replace it, the water may either force its way out, or fill the toilet bowl and run out.

Maybe look at the mobile home thing.

labman, when a situation arises that water is coming back from a sewer it indicates the floor level is lower than the level of the street level and there is either a slow sewer on the municiple side or the sewer is under sized. In either case when even a small amount of rainwater is added it backs up. This backed up water seeks a level to escape. Typically it escapes through a manhole cover. But if your home floor level is below that level it is required that you have a backwater valve. It can be installed inside the home for depth access or outside. I have seen them in boxed areas inside a basement. The depth was only a foot or so under the slab. Either case, when the neighborhood sewage can or may back up into a dwelling, that dwelling must have a backwater valve.

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Originally Posted by doug238

growler got it. the backwater valve also must be accessable for maintanance

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That's not really feasible is what I was trying to say... accessibility to a pipe buried 8 feet into the ground isn't really possible at all... and labman, thanks, but I'm not sure the wife would appreciate me putting in one of those ugly (and small) rv toilets in our bathroom... is there an alternative I should be looking at that would provide the same function without the un-pleasing asthetics?

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Originally Posted by doug238

labman, when a situation arises that water is coming back from a sewer it indicates the floor level is lower than the level of the street level and there is either a slow sewer on the municiple side or the sewer is under sized. in either case when even a small amount of rainwater is added it backs up. this backed up water seeks a level to escape. typically it escapes through a manhole cover. but if your home floor level is below that level it is required that you have a backwater valve. it can be installed inside the home for depth access or outside. i have seen them in boxed areas inside a basement. the depth was only a foot or so under the slab. either case, when the neighborhood sewage can or may back up into a dwelling, that dwelling must have a backwater valve.

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I was aware of all that. Are you aware that there are millions of houses that were built without them and in many cases retrofitting them would be a large project?

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Originally Posted by labman

retrofitting them would be a large project?

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Large for you, impossible for me lol

Not all problems have a reasonable solution. Fix the leak between the toilet and floor, and the water may come out the top of the bowl. If the flap you hope for exists, stop the toilet and the water may come out the lavatory. There is a prohibited connection between your sanitary sewer and the storm drainage. The storm drainage is inadequate. Neither of those will be cheap and easy to correct.

How old is the house and how long have you owned it? Some times somebody else is responsible for correcting a big expensive problem. We have a real estate law forum here.

If water can leak out between the floor and toilet, so can smelly, toxic sewer gas. You only have 2 bolts and one water connection holding the toilet in place. A new wax ring is chicken feed. You need to do it whether it will fix the water problem or not. It could if the nearest man hole cover or curb drain is between the floor and the top of the bowl.

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Originally Posted by labman

I was aware of all that. Are you aware that there are millions of houses that were built without them and in many cases retrofitting them would be a large project?

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Hmmm...

A "large project" versus raw sewage backing up into the house.

"Large project" wins out in my book, Labman.

It's not "raw sewage"... it's always clear water, presumably rain water... it doesn't have an odor but we still have to quarantine the area and anti-bacterialize everything...

labman... we've lived in the house for almost a year, it was built in the late 60's if I remember correctly... I was planning on replacing the ring either way but I was hoping to have something to shove in-line maybe as some sort of check valve...

Many homes have storm water connected to the sanitary sewer and if there is a partial blockage in the sanitary sewer it will cause the symtems you describe.
The next step should be to have a Close circuit TV inspection from the cleanout out to the sewer in the street.
If the City has been out 4 times in five months they should be able to tell you what and where the problem is.
I am in charge of the a sewer collection system with about 50,000 connections and that is my number one tool for discovering the problems.
The City may do it for free if they have found the blockages on City property. Believe me they don't want to keep sending crews out to clear sewers any more than you want them there.
If the City won't come out most plumbers can televise the line for you.
Your original question: Is there a flap on the line for the toilet. No there isn't
The backwater valve is only effective in situations where the sewer main on the street is surcharging causing the sewage from the street to back up into the house.
It will not work if the blockage is in your individual service.

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The backwater valve is only effective in situations where the sewer main on the street is surcharging causing the sewage from the street to back up into the house.
It will not work if the blockage is in your individual service.

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Be that as it may, all three of the major Plumbing codes adopted for use in the US require a backwater valve for any drainage piping serving fixtures that have flood rim levels located below the elevation of the next upstream manhole cover of public or private sewers.

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it's not "raw sewage"... it's always clear water, presumably rain water... it doesn't have an odor but we still have to quarantine the area and anti-bacterialize everything...

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You say it isn't raw sewage because you don't see any brown trout leaping majestically across the linoleum, right?

If it is backing up through a line used for the discharge of raw sewage... Then what is backing up through the line is raw sewage -- It may very well be co-mingled with rain/ground water, but it's still raw sewage.