Help with RV drain problem

We defiantly stay hooked up, as when we stop, we stay for several weeks at a time. This is the second year we have had them. They cam last year, and we thought they went away, but then at the same time again, they came back. It is like their eggs were hibernating for the winter and when spring came, so did they :(
We have been buying the fly strips to catch the adults, which have helped. To get rid of them, we have tried spraying bug spray, pouring vinegar and baking soda down the drains to clean them, and even put bleach down the toilet, but they still come back.
Hopefully, your ideas will work ((crossing fingers))!


Thank you everyone for your help :)

I had them in the black tank twice in 12 years and that valve is closed except for a minute so while dumping so they are probably coming in the roof vent and laying eggs in the crud on the tank walls.
I killed them with bug spray through the toilet flush hole.

When I got them in the shower I poured boiling water down the drain a few times and that killed them.

If you want to leave the stinky slinky hooked up, be SURE to put a P trap in it either below the RV, or at the dump site. I use a big rock, if available, to do that. If I can't find a big rock, I take 3 of my leveling blocks and make one.

This is not my rig, I found it on the internet, but it shows what I am talking about.

I find that I have to kill two or three generations of the things before they are gone. They do show up in certain places if I leave a hose connected, even if valves are closed, so I don't really do full hookups anymore. If there is a sewer connection at my site I use it as a dump station rather than hooking up longer term.

Drain flies live in the gunk that builds up in your drain pipes BEFORE the P trap. Clean the pipe out with a drain brush or take it apart and use an old toothbrush. Get all of the gel looking stuff off(that is where they lay their eggs). That should take care of the next generation. For a non-toxic way to get rid of the adults, put a shallow bowl of cider vinegar with a squirt of dish soap in it. The vinegar will attract them and the soap will kill them.I had them in the house and this worked for me.

Wonder what would happen if.......

Put a 5" Clear extension on the tank outlet,,, DRAIN TANK and rinse, leave the extension on the tank and let it drain till it's all gone. Put one of the "Flush King" type vlaves (Link will be added shortly) The one I pictured is not the one I'd use if you have a tank flusher but if you don't .. Well then it IS the one I'd use.

(The one I would use (I have the Tornado tank flusher) is just the valve, no elbow, no "inlet" Pug this on the bottom of the 5".

Now, Remove the hose. Trigure a bug bomb, shove it up into the extension, and CLOSE THE VALVE below it..... GO, Look, See (Sights) dine (OUT) whatever, Come back, close main tank valve (The one you have, if there is any liquid in the extension hook up hose and open valve part way so it drains, Remove extension (Close valve first) and wearing gloves remove bug bomb, double bad and disopose of (Along with gloves) following good haz-mat procedure. Re-attache hose and other accessories as desired.

they shouldn't be able to come up through your trap.

Fill your gray and black tanks with water and add bleach.

they should feel the LOVE...very quickly..

Don't leave waste tank dump valves open........you are just inviting them to come into your waste tanks and set up house.
Only dump when tanks are almost full or full.

Get some bug spray
Turn off water...open toilet and spray down into tank and all around. CLOSE toilet and then turn water back on and put some water in toilet bowl.
Wait several hours..longer the better before using toilet.

You may have to go on roof and spray some down vent pipe(s)

Run some water down sink/shower drains to make sure 'P' traps have water in them.