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Old 06-05-2012, 03:43 PM   #1
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gray water

Hi, I keep our gray water valve open all the time. someone told me that sewer gnats can come in through the toilet. I have been suffering with allergies and itching since I have been living in this rv. Does anyone else have this problem.

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Old 06-05-2012, 03:49 PM   #2
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Most say to keep your valve closed until 3/4 full. That way you get a good strong flow when dumping.

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Old 06-05-2012, 03:56 PM   #3
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Sorry to hear of your allergies and itching. You don't mention anything about your RV, but if it is brand spanking new maybe carpet, adhesives or some other irritant is bothering you? If its a used RV maybe the pervious owners have left their mark with an irritant such as pets or smoke?
We leave both the black and grey valves closed until dumping.
I am sure you will hear plenty of good advise on the method of black and grey valve operation from fellow posters.
Good luck!
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Old 06-05-2012, 03:58 PM   #4
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Gray tank is not connected to the toilet. The black tank is.Sinks, shower drain into the gray tank. However, it is possible for all type of bugs to come in through the drain into the open gray tank and then through the drain system.

Many people keep the gray open, many do not. If you think you are having issues then I'd suggest closing them and dump the gray every other day or so. Let it fill up prior to dumping the black tank. Wait till the black is 2/3 to 3/4 full dump the follow by dumping the gray.
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Old 06-05-2012, 06:26 PM   #5
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Campers are notorious for having high levels of formaldehyde. Not sure if there is a way to test for that but you could check
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Twenty years from now you'll be more disappointed by the things you didn't do than by things you did. Explore, Dream, Discover. Mark Twain
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Old 06-05-2012, 06:32 PM   #6
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If your sewer hose has a tight seal to the dump opening (which it should), I'm not sure how you would get bugs into the tank in the first place. And not to the toilet, since your black tank valve would be closed. And all the gray tank drains should have p-traps in them.

So, I think that story is an urban legend.

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Old 06-05-2012, 07:45 PM   #7
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Originally Posted by FlyingDiver View Post

So, I think that story is an urban legend.

I agree, someone is pulling your leg. Toilet bowl is closed to the black tank until you flush. Each drain has a trap that goes to the gray tank. IF insects were a problem, a simple dip/low spot in the drain line would create a 'trap' to prevent entrance of bugs. Don't get sold a 'Left handed smoke shifter' for your campfire, or go on a snipe hunt.

If you are at a campground with a sewer hook up, it doesn't hurt to leave the gray tank valve open. It's a good idea to close it a day or so before you plan to dump the black tank, then you can use the gray to flush the slinky after dumping the black.

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Old 06-06-2012, 10:45 AM   #8
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I have had sewer flies three times in ten years. Two times they came up through the shower and the other through the toilet. There is always water in the gray water P traps since we full time.

Sewer fly larvae live in the slime coating the sewer pipes, external and internal. When they change to flies they come out of the drain. I do leave the gray water drain open until 3 days before I dump the black tank.

The P traps don't seem to stop them. One poster said that part of their life cycle requires them to be in water but I have not been able to verify that.

It's easy to get rid of them in the shower drain. As recommended by a site I found when Googling them, just pour a pan of boiling water down the drain, wait a day or so and repeat.
I had the little boogers in the shower this week and just poured the boiling water down the drain the second time yesterday.

When they came out of the toilet when it was flushed I sprayed a lot of insecticide on the tube that goes from the toilet down through a grommet in the top of the tank and in the tank itself. That got rid of them.
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Old 06-06-2012, 12:09 PM   #9
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Sewer flies can come up through an open connection into the coach. My friend Joe had that happen to him. Upon arrival, he hooked up and left the gray water valve open. The next day we all went out for the day and when we came back, his coach was full of the things! Horrible!

People don't always put the cover plate on the sewer drain back on leaving it wide open to whatever. When you connect to the drain and leave your valve open, you are wide open for entry into the system in my opinion. After Joe's experience I will never leave mine open, never. We figured that possibly one of the p-traps had lost the water in it while driving. I always keep mine closed unless dumping.
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Old 06-06-2012, 12:47 PM   #10
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Your tanks and internal waste pipes are open to the roof vent tubes so anything flying around outside has access. The RV parks that have septic systems are also vented to the atmosphere in many cases.

I have only had the problem three times in ten years and rather than dump my gray tank every fourth day I will leave it open and take my chances.

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