Strange problem with gnats in bathroom

[KathyandMark]

Hi everyone, we're a bit stumped here. We have a 2013 FR Georgetown,335 DS. It's been a great RV, no problems, no leaks, bought it used and fully inspected it my a certified RV inspector .About about a month ago, after returning from an RV trip to New Orleans, we stored our RV as normal, outside in a RV parking lot near a woody area. Checked in on it a week later, and found a large amount of teeny dead gnats in the shower floor and some gnats flying near the ceiling. They are nowhere else in the the RV. In an effort to figure out whats going on, we tried a few things to find the problem : resealed the skylight above the shower, put tape over all drains in the bathroom to see if the gnats were coming from them (they are not ), did a black water flush 3 x's to see if the problem might be sewage gnats. After the flush, there is some improvement, but we still have about 1/4 of the gnats than we first had originally
We also have found a couple of gnats in the toilet. The seal in the toilet is tight. Any ideas on what else we can do for this? Thanks so much for your help!

[Ray,IN]

I suggest, first drain the black tank completely, use an aerosol can of flying insect killer to thickly fog the black tank via the now-open drain valve. Something solid needs to be made(plastic) to seal the 4" opening with a 1/2" hole in the center.
I think what you have are sewer flies, they are tiny and black. Quickly replace the sewer cap, don't disturb the black tank for a day if possible. This kills the adults but not the eggs, so a repeat may be necessary 2-3 days later.
Sewer flies come from the CG sewer system. I've had them 2X. Aggravating to say the least. DW is a germaphobic, so I don't delay any remediation.

[Jay D.]

How do they get from the black tank up through the toilet seal and water to the inside. i'm wondering, do you have a vent or window open were they can sneak in.
Jay D.

[Rickho]

When you’re camping, do you leave the black and gray tanks hooked up and open full time?
I’ve seen those little black fly’s in some of the drains where weather was hot and humid.
I don’t open or hookup to the drain until I’m ready to dump the tanks. This keeps the flys out of my system.
Of course they could always be coming in from the black tank roof vent pipe but I would expect they got in from the drain while you were hooked up.
I make a habit out of hooking up only when ready to dump then unhook the flex drain pipe when done. The last suggestion for fogging the tank is the way to get rid of what’s in the tank now.

[sdennislee]

I've had them twice, both times in Florida, both times from the gray tank.

I read somewhere the larva can swim so P traps become a little useless if this is true.

I always create a trap in my sewer hose, see my point above about larva swimming.

The adults I killed with Pest strips hanging in the bath room and 2 bowls of apple cider vinegar and dish soap covered with plastic wrap. I used between 1/4 cup to 1/2 cup of apple cider vinegar plus 3 to 5 drops of dish washing liquid, covered that with the plastic wrap and poked 4 or 5 holes in it. Each morning I would 30 to 50 dead sewer gnats in the bowls.

To kill the eggs I thoroughly rinsed the gray tank using bleach.

Then kept the gray tank valves closed until it was time to dump. No more gnats. As a rule now when in Florida at this park I keep the gray valves closed. Most other places I leave them open.

If you've tape up the drains securely and the toilet has a good seal I have no clue how they are getting in, perhaps like a mouse squeezing through a 1/4" opening the gnats can squeeze past the seal or under the tape.

The apple cider vinegar with dish washing liquid will help you get rid of the ones that are there now can't help with the prevention other than what I've already said about valves closed.

From one of the articles I read, this shows why you have to be persistent, not a one day battle.
"Thankfully sewer flies do not bite, but they can be very annoying and still even dangerous at times. Because they are born among decaying filth and waste, they have the capability to transmit diseases to humans. Prolific little creatures, they lay their eggs in masses of anywhere from 10 to 200 groups, according to one report I researched. The larvae resemble small worms; basically without legs. The eggs can hatch anywhere between 32 to 48 hours. They mature in about two weeks and simply keep reproducing until they die or are eradicated. But keep in mind, new adults keep emerging from the pupae every 20 to 40 hours! The adults live approximately two weeks."

[Gary RVRoamer]

It sure sounds like sewer flies, and they seem to get by most attempts to seal them out. They breed in either gray or black tanks and it takes repeated spray/flushes to get rid of them because more larvae hatch after each attempt. The larvae are safe in the slimy residue on tank walls, around valves, etc., so you need to repeat the process every couple days for awhile to kill them off as they emerge.



Insecticide in the tanks helps kill off the adults and flushing gets rid of some of larvae, but it takes repeated applications to get them all and break the breeding cycle.

[FatChance]

Good reason to keep black and grey tank flush valves closed.

[KathyandMark]

Thank you Ray, IN - we are on our way to the RV in a few minutes to try your suggestions. This forum has been so helpful. Were taking everyone's suggestions in, and hopefully, we'll be able to get rid of these gnats. Thank you so much.

[KathyandMark]

Jay D - thank you for your response. We are wondering if a little vent that is from the refrigerator that goes into the bathroom might be the culprit. To find out for sure, we are going to seal that vent up for the time being, along with the other remedies here, to see if we can't do this by process of elimination. Thank you so much

[KathyandMark]

Originally Posted by Rickho

When you’re camping, do you leave the black and gray tanks hooked up and open full time?
I’ve seen those little black fly’s in some of the drains where weather was hot and humid.
I don’t open or hookup to the drain until I’m ready to dump the tanks. This keeps the flys out of my system.
Of course they could always be coming in from the black tank roof vent pipe but I would expect they got in from the drain while you were hooked up.
I make a habit out of hooking up only when ready to dump then unhook the flex drain pipe when done. The last suggestion for fogging the tank is the way to get rid of what’s in the tank now.

Rickho, Thank you, yes, we close up the black and gray tanks when we camp and only open them up when we drain. Thank you so much.

[KathyandMark]

Originally Posted by sdennislee

I've had them twice, both times in Florida, both times from the gray tank.

I read somewhere the larva can swim so P traps become a little useless if this is true.

I always create a trap in my sewer hose, see my point above about larva swimming.

The adults I killed with Pest strips hanging in the bath room and 2 bowls of apple cider vinegar and dish soap covered with plastic wrap. I used between 1/4 cup to 1/2 cup of apple cider vinegar plus 3 to 5 drops of dish washing liquid, covered that with the plastic wrap and poked 4 or 5 holes in it. Each morning I would 30 to 50 dead sewer gnats in the bowls.

To kill the eggs I thoroughly rinsed the gray tank using bleach.

Then kept the gray tank valves closed until it was time to dump. No more gnats. As a rule now when in Florida at this park I keep the gray valves closed. Most other places I leave them open.

If you've tape up the drains securely and the toilet has a good seal I have no clue how they are getting in, perhaps like a mouse squeezing through a 1/4" opening the gnats can squeeze past the seal or under the tape.

The apple cider vinegar with dish washing liquid will help you get rid of the ones that are there now can't help with the prevention other than what I've already said about valves closed.

From one of the articles I read, this shows why you have to be persistent, not a one day battle.
"Thankfully sewer flies do not bite, but they can be very annoying and still even dangerous at times. Because they are born among decaying filth and waste, they have the capability to transmit diseases to humans. Prolific little creatures, they lay their eggs in masses of anywhere from 10 to 200 groups, according to one report I researched. The larvae resemble small worms; basically without legs. The eggs can hatch anywhere between 32 to 48 hours. They mature in about two weeks and simply keep reproducing until they die or are eradicated. But keep in mind, new adults keep emerging from the pupae every 20 to 40 hours! The adults live approximately two weeks."

Dennislee, thank you for your suggestions. We are going to try the apple cider and dish soap remedy today, along with everyone's suggestions on here. This is pretty serious, germs in the sewage is nothing to mess around with. Thank you so much!

[SuzanneH]

I turned the water off to the coach, held drain pedal open and sprayed ant spray in the pipe and up under the flap as much as I could. Problem solved.

[SarahW]

When our RV is in storage, I make sure there is water in the p-traps under ALL drains... sinks and shower. I bought a 4" flat disk type "stopper" to cover the shower drain and I close ALL stoppers in all the sinks. That way if the P-traps should dry out, the sinks are stopped up and nothing should be coming in/out of plumbing drain pipes. (This also prevents any smells that could enter the coach in hot weather when p-traps could dry out.) Make sure there is plenty of water sealing the toilet bowl, too.

Those gnats are the main reason we do not ever leave our stinky slinky hooked up at the campground. We only hook up to dump, then rinse and put away the hose.

[Ray,IN]

Originally Posted by Jay D.

How do they get from the black tank up through the toilet seal and water to the inside. i'm wondering, do you have a vent or window open were they can sneak in.
Jay D.

Every time you flush, it gives them an opening. Most rv toilets have a small opening under the rim to prevent overflowing.