Go Back   iRV2 Forums > iRV2.com COMMUNITY FORUMS > iRV2.com General Discussion
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
Thread Tools Search this Thread Display Modes
Old 09-02-2016, 10:57 AM   #1
Moderator Emeritus
smlranger's Avatar

Country Coach Owners Club
Freightliner Owners Club
Join Date: Sep 2004
Location: Glen Allen, VA
Posts: 7,471
Blog Entries: 1
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.

'07 Country Coach Allure 470 Siskiyou Summit #31578, Cummins ISL 425; 2014 Ford F150 toad; Air Force One Toad Brake.
Glen Allen, VA; Smith Mountain Lake, VA.
smlranger is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 09-02-2016, 11:17 AM   #2
Senior Member
bud01234's Avatar
National RV Owners Club
Join Date: Jun 2015
Location: florence, Ky
Posts: 166
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.

1998 National Dolphin 36' 5360 GM with tag axle.
Using my segway for a toad.
bud01234 is offline   Reply With Quote
Old 09-02-2016, 11:31 AM   #3
Senior Member
Join Date: Nov 2015
Posts: 5,468
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)
Old-Biscuit is online now   Reply With Quote
Old 09-02-2016, 11:32 AM   #4
Senior Member
JJH3rd's Avatar

National RV Owners Club
Workhorse Chassis Owner
Join Date: Feb 2011
Location: Covington, GA
Posts: 536
Send a message via Skype™ to JJH3rd
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.
J.J. Hayden (KN4SH)
Covington, GA
2005 National Dolphin 5342
JJH3rd is offline   Reply With Quote
Old 09-02-2016, 02:07 PM   #5
Senior Member
Workhorse Chassis Owner
Join Date: Jun 2003
Location: Palisade CO
Posts: 3,579
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.
Clay WA5NMR - Ex Snowbird - 1 year, Ex Full timer for 11 years - 2004 Winnebago Sightseer 35N Workhorse chassis. Honda Accord toad.
Clay L is offline   Reply With Quote
Old 09-02-2016, 03:36 PM   #6
Senior Member
Join Date: Aug 2011
Location: Enjoying the Western States!
Posts: 6,425
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.
Full-timed for 16 Years . . . Back in S&B Again
Traveled 8 yr in a 2004 Newmar Dutch Star 40' Diesel
& 8 yr in a 33' Travel Supreme 5th wheel
twogypsies is offline   Reply With Quote
Old 09-02-2016, 04:14 PM   #7
Senior Member
sdennislee's Avatar

Monaco Owners Club
Winnebago Owners Club
Join Date: Sep 2011
Posts: 6,859
If you do continue to keep the grey tank valve open, create a P trap in your sewer hose
US Navy Vet, Liberty Tree Member of Oath Keepers, NRA & VFW Life Member, Alaska EMT.
2009 Safari Cheetah 40 SKQ
2009 Winnebago Chalet 231CR
sdennislee is offline   Reply With Quote
Old 09-02-2016, 07:34 PM   #8
Senior Member
Join Date: May 2011
Posts: 1,039
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.
jpharley is offline   Reply With Quote
Old 09-02-2016, 07:42 PM   #9
Senior Member
dennis45's Avatar

Join Date: Jun 2012
Location: BC
Posts: 6,956
Valves closed until the tanks are at least 3/4 full on BOTH tanks.

Dennis & Carol
Said so long to our DSDP. Coming Soon, 2019 Unity LTV CB - 2013 Honda CRV, BlueOx Baseplate, Aventa Bar & Patriot Brake. And the 04 Bird
dennis45 is online now   Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Sewer flies in black tank rgriff Class A Motorhome Discussions 1 08-27-2016 12:35 PM
Fruit flies, gnats or whatever TexasTwoStep Excel Owner's Forum 7 11-03-2014 04:45 AM
Drain Flies?? Clayobx MH-General Discussions & Problems 5 05-28-2014 05:25 AM
Screening GNATS!! Chickadee Newmar Owner's Forum 6 07-08-2010 10:13 AM
Gnats, Black Flies or No See-ums motojavaphil Just Conversation 5 07-03-2009 09:47 AM

» Featured Campgrounds

Reviews provided by

Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 01:32 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.