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Old 09-02-2016, 10:57 AM   #1
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Sewer gnats, drain flies??

We've been on the road for about two weeks and today DW opened shower door and a bunch of little black gnats flew out. I'm thinking they must be coming from the sewer? Other than keeping the gray water valve shut until the tank is full, is there anything I can do to get rid of them?

Like most folks, we leave the BW valve shut and the GW valve open.

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Old 09-02-2016, 11:17 AM   #2
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If the little gnats bother her, she'd really freak out if a rat or other varmint from the sewer invited himself in via a line left open to the sewer.

I keep both valves closed until time to dump. Sometimes you may have to dump grey tank alone but that's not a big deal.

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Old 09-02-2016, 11:31 AM   #3
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Sewer flies/gnats is one reason to LEAVE dump valves closed until time to dump (and a good reason at that)

Now that you have them.they have set up house in your grey tank and have invited all their cousins and ner-go-wells to come live with them.

You will need to fill grey tank FULL (VERY FULL) with a strong bleach concentration (1 cup/20 gallons---let sit for at least 1 hour) to kill them off but they may have set up condos in vent line.
Better get a 'bug bomb' and set it off in vent line

Adults live 20-40 hrs but eggs (1000's) hatch every 32-40 hrs so they just keep on coming.......

LEAVE the dump valves closed.

But if you really really need to have grey dump valve open make a 'dip' in sewer hose and fill with water. (P Trap so they can't come visit)
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Old 09-02-2016, 11:32 AM   #4
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A couple of summers ago, we were staying for 3 weeks at a campground. About half way through we begin to do battle with large house (RV?) flies. I traced the invasion to the sewer hook up. I had, like you, the BW valve closed and the GW valve open. Since there is only 1 sewer connection at the park, and the flies seemed to come out of the bathroom (I saw a couple emerge at different times). I deduced, like you, the source was the sewer connection. My solution was to only open the valves when I dumped the tanks. This solution (procedure) seems to be working.

The problem is that my (our?) sewer hoses have no "trap" between the RV and the camp sewer pipe. The "U" bend in the pipes under sinks, usually holds water and keeps (in the house) sewer gas from coming up the drain (and also any flying things that aren't amphibious).

So far I have had no invasions of thongs that were able to swim against the flow of black and the Gray water when I dump the tanks.
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Old 09-02-2016, 02:07 PM   #5
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To kill them you can pour boiling water down the shower drain. Might have to do it twice but it worked for me.
I don't think keeping the dump valves closed will help. I had them in the toilet once and that valve was only open when I dumped. I am thinking that they might fly down the vent pipe into the tanks.
I think that they can get from the tank through the water in the traps while in the larval stage and pupate in the gunk on the shower drain or tank walls in the case of the toilet.
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Old 09-02-2016, 03:36 PM   #6
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I've read that some folks think they can also come in through the toilet vent on the roof. We never had them so don't know.
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Old 09-02-2016, 04:14 PM   #7
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If you do continue to keep the grey tank valve open, create a P trap in your sewer hose
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Old 09-02-2016, 07:34 PM   #8
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We have property in the Midwest and the local sewer and storm water drains are the same piping and are often overwhelmed. We discovered that during heavy rain, the water was trying to back up through our sewer hose and thank goodness, we had the valves closed or it would have been inside the RV. Another reason to keep the valves closed until ready to dump.
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Old 09-02-2016, 07:42 PM   #9
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Valves closed until the tanks are at least 3/4 full on BOTH tanks.

Dennis & Carol
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