Black flying insects in the bathroom

[Kasey]

I am currently camping in NW Iowa in my 04 Dolphin. I have had this happen before but not to this extent. When I raise the toilet seat and run water a bunch of black flying insects come out of the toilet. The toilet is holding water so it is sealed. The motorhome is closed up with the AC on. I’m trying to figure out where they are coming from and how to get rid of them! Thanks

[keymastr]

If you leave the black tank valve open then sewer flies can come up into your plumbing system. You should put half a tank or more of water in your black tank and 2 cups of bleach flushed down the toilet and let it sit for a few days until nearly full. Leave it for as long as possible, the chlorine gas will kill whatever is living in your tank. Then dump and close the black tank valve, add several gallons of water down the toilet and that should take care of your issue.

[Kasey]

Thanks for the reply! I never leave any valves open unless I am dumping and haven’t seen any come out of the actual toilet sewer pipe when I flush but they congregate under the lip of the toilet. The toilet is holding water so if they are sewer flies I can’t figure out how they are getting into the toilet.

[MikeandRuth]

We get them in warm weather also. We think they come in thru the window screen. I am convinced I have seen them come thru the screen. Spray the screens and around the stool and see if it helps. That is what we do! Good luck.
And, we never leave the black tank valve open and our stool holds water also.

[CampDaven]

They will come in through your tank vents on the roof. A vent screen is needed

[Kasey]

Originally Posted by CampDaven

They will come in through your tank vents on the roof. A vent screen is needed

Do they sell vent screens or do I need to make one?

[CampDaven]

Originally Posted by Kasey

Do they sell vent screens or do I need to make one?

I’ve not had the problem but other campers have. I know one got screen material at a hardware store.

[Glamping2]

I’m sure this is right they are coming down your vent stack for your waste tank a piece of screen placed over the stack should solve this.