November 2009 RV Doctor Frustrating Fly Infestation
This article was in response to purchaser of used motorhome who tried using half gallon of ammonia; without success.
www.fmca.com/index.php/house-calls/2871-house-calls-november-2009 Now, on to your bug problem. Evidently you are experiencing an onslaught of sewer flies, also called drain gnats, among other names (some of which cannot be printed here). Depending on your specific variety, the scientific name is probably either Psychoda alternata or Psychoda cinerea. They are sometimes found in RV holding tanks, since they thrive on moist organic waste, especially solid waste. Just the kind of stuff you’d find in a black holding tank, particularly one that has not been cleaned, flushed, or maintained adequately. Chances are, at some point, your new-to-you motorhome was probably stored without the holding tanks being flushed, cleaned, and emptied completely.
Thankfully, sewer flies do not bite, but they can be very annoying and even dangerous at times. Because they are born among decaying filth and waste, they have the capability to transfer bacteria to kitchen surfaces, etc. Prolific little creatures, they lay their eggs in masses of anywhere from 10 to 200 groups, according to one report I researched. The eggs hatch approximately 32 to 48 hours after being laid, and the larvae resemble small worms. The flies mature in about two weeks and simply keep reproducing until they die or are eradicated. Keep in mind, new adults continue to emerge from the pupae every 20 to 40 hours! The adults live approximately two weeks.
For short-term relief, published reports recommend using a spray can of an insecticide containing pyrethrins (natural insecticides produced by certain species of the chrysanthemum plant) or resmethrin. A treatment using this type of insecticide should knock the adults down for a while. I must admit, however, that I’ve never personally tried the insecticide route. If you do, always follow the proper safety precautions for pesticide use, especially inside the motorhome. After killing the flies in the immediate area, be sure to sufficiently vent the entire RV. Read the precautions on the spray can carefully.
But the best defense against long-term infestation is to simply keep the holding tanks flushed and clean during periods of nonuse. In your particular instance, it may be necessary to have your holding tanks hydro-cleaned (visit
www.allprowaterflow.com for information about one company that performs this service). Because dried waste can stick to the sides and bottom of the holding tank or clog the tank outlet, simply draining and flushing with fresh water may not be enough to dislodge all contaminants. And as you flush the toilet, the added moisture imbues new life into the larvae, prolonging the infestation. The bottom line is that the toilet drain and the black holding tank must be thoroughly cleaned prior to placing the motorhome in storage.
Although some people may not favor a holding tank additive, the proliferation of sewer flies is one strong case to indeed employ one. An enzyme-based, formaldehyde-free additive, one that helps digest the solids, is my recommendation. I’ve personally seen an infestation so severe that the flies had backed up into the integral tubing inside the toilet. The toilet had to be completely disassembled, cleaned, and reassembled. It was quite time-consuming. I hope your situation isn’t that bad. But it does mandate at least a complete inspection of the toilet and other components, such as the vent pipe for the black holding tank. It’s not the end of the world, obviously, but it is quite annoying.
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