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Old 09-24-2020, 07:04 AM   #1
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Sewer/Drain Flies

We have reworked our whole sanitary system, new Atlantis Freedom heads, new hoses, installed new 1 inch vent hoses through straight mushroom thru hulls both port and stbd, and a Groco Sweet Tank in. 40 gallon tank. Only treatment is Raritan .K.O. and C.P. Works great, always dump before getting within 3 inches of top of tank. Only issue is we now have issues with sewer flys. They love it inside the tank and swarm around the new vents. Had a small pin-hole opening in top of tank and flies are now in the boat.......pin-hole fixed.

What’s the best method to eradicate these pesky flies from the tank and from the inside of the boat. Fly paper is working OK inside as does tray of vinegar, just concerned the vinegar is an attractant.

Thoughts?
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Old 09-24-2020, 09:26 AM   #2
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We sometimes get those small fruit flies in our house in the summer.

Get a glass jar, pour in some apple cider vinegar and a drop of dish soap, put it in a plastic bag, push the top of the bag down to just over the liquid so it is funnel shaped, and poke a hole in the bottom so the flies can get in.

Give it a day or so before you check...lotsa dead flies!
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Old 09-24-2020, 09:56 AM   #3
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Thanks - we have been using the vinegar method with some success, however I’m more seeking a solution for the source. I suspect this could be a battle that can not be won, however thought someone out there may have a “trick”. I did read about filling the tank to “full” with a mixture of bleach to kill-off the eggs and larva, however that would be a one-time shot solution, and the problem could reoccur.
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Old 09-24-2020, 11:37 AM   #4
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Drain flies are bigger than fruit flies and have black wings. When you smash them on the wall, you'll see that they leave a black smudge.

Drain flies depend on the organic material that builds up in drains/tanks to live and breed. Drains are the most common source, but also inspect your holding head/tank just in case.

A couple of ideas to track down the source, or sources; Smear a little Vaseline inside solo cups and place them upside down over the drains, or, seal drains with clear tape, sticky side down, poke a few air holes so they still try to exit. Leave the traps set overnight (or longer) as they are more active at night. When you identify the source drains, you are on the hunt!

Drain flies have a fairly long life cycle of 1-3 weeks, so you need to wipe out the egg cycle (~48 hrs), larvae stage (~12-14 days) and breeding adults all at the same time to be fully rid of them.

Clean the suspect drains with your drain cleaner of choice. Bleach may kill the larvae on contact, but if the food source remains, you are still subject to new outbreaks if you still have adult flies around. Once the drains are cleaned, I suggest keeping a cup over the drain opening whenever the drain is not in use for several weeks until the life-cycle is broken and you don't see any more flies.

Good luck!
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Old 09-24-2020, 03:27 PM   #5
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Buy a pet bat. They love flies and have interesting habits and some people like to eat them!
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Old 09-24-2020, 05:43 PM   #6
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Xs,
I am not letting you anywhere near my dog Too funny
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Old 09-25-2020, 06:16 AM   #7
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A very fine screen in the waste vent should keep new airborne visitors out.

The nicest very fine SS screen I have seen is an IKEA fry pan splatter screen, $5.99



IKEA - STABIL Splatter screen, stainless steel, Diameter: 13 "
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Old 09-25-2020, 07:10 AM   #8
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Consider spraying one of the pyrethin insecticides into drains and vents. If breeding in your tanks a larvicide may work. Used mostly for mosquito control. I saw a Bayer product that was labeled for sewage applications.
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Old 09-25-2020, 08:10 AM   #9
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Quote:
Originally Posted by FF View Post
A very fine screen in the waste vent should keep new airborne visitors out.
Nice find.

A general question though: Would the reduction in air flow caused by a screen be an issue for the holding tank vent to do its thing? I mean, I realize it would still allow air in to keep the tank from collapsing; but what about the "action" that the tank needs via airflow?

Reason I ask is because for example if you use no-see-um (very fine) mesh instead of normal screen on your windows, it cuts the air flow down substantially.

********
I have noticed that dessicating toilets specify a screen on their vent (to keep sewer flies out), but they seem to also want you to have an exhaust fan on the vent going 24/7 so that might get around the restriction of the screen (the hose also looks like it is 2+" in diameter).

The dessicating toilets also say you can add diotomaceous earth to "cut" the flies and larvae to death, but I guess that would be difficult to implement on a liquid filled tank you are pumping regularly.
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Old 09-25-2020, 08:25 AM   #10
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Ordinarily I'd say the the mesh would be a restriction issue, but with 2 good size vents plus a sweet tank system providing a bit of forced ventilation, the tank should still get plenty of air.
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Old 09-25-2020, 08:37 AM   #11
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Good discussion folks, thanks! I had similar thoughts on screen restrictions, however agree the Sweet Tank will keep positive pressure in the tank and 2 independent 1" vents provide a pretty good opening to work with ......its worth a trial test!
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Old 09-25-2020, 08:54 AM   #12
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Ordinarily I'd say the the mesh would be a restriction issue, but with 2 good size vents plus a sweet tank system providing a bit of forced ventilation, the tank should still get plenty of air.
Thanks for reminding me that the OP has those improvements. I got focused on the flies and the mesh and forgot about that from the first post
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