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Old 10-20-2020, 08:59 PM   #1
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Unhappy Yuckie odor coming from Gray Tank exhaust

Thanks to the health "situation," we've ended up in a nice little RV Park on a semi-long term basis. Recently, we have noticed a sewer-like odor in the evening around our rig (Class C 05 Winnebago Itasca). We had someone look at the exhaust pipe on the roof and he confirmed that the odor was coming from the gray water tank. (We have a compost toilet and the black tank is hermetically sealed -- no odor there.)

We keep the drain on the gray tank open and run a good flush of water through it nightly, but the odor comes back after a day or two. There is no flush hose opening in the tank. I've tried gray tank solutions, baking soda & vinegar, closing the tank for a few hour while the solutions sit and gurgle, then flushing it profusely from the sinks inside. Again, the odor starts to appear in a day or two.

Am at my wits end. We have double screens over the inside drains so junk doesn't fall into the drains. Help!
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Old 10-20-2020, 09:08 PM   #2
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Welcome to iRV2 .
Sorry your first post is about problems.

If your leaving the grey dump valve open ; the whole park sewer system can vent through your tank .

Close the valve use the tank till it's 2/3, 3/4 full then dump .
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Old 10-20-2020, 09:36 PM   #3
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Yep, keep the vavle closed until you're ready to dump. Dump and close.
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Old 10-20-2020, 09:43 PM   #4
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We had the same problem. There are several posts here on IRV2 that talk about items to check that may be causing gray tank gas to enter the MH. There are plenty of items to check. One solution we found was to close all the windows and roof vents when driving. Having windows or roof vents open create a vacuum in the MH and suck the gases into the MH. One other thing we did was to clean the inside of the tank. Prior to going on a trip, I filled the gray tank 3/4 full. Then I added 5 Gallons of 409 cleaner, and drove to our destination. I dumped the tank when we arrived and it was much cleaner smelling. We now add 3 oz of Pure Power Blue to our tank and leave the valve closed until the tank fills to between 3/4 and Full, then dump and add another 3 oz of Pure Power. If we're somewhere that's hot we may add an additional 3 oz of Pure Power between dumping.
If you prefer to leave your gray tank valve open while parked, you can put a short 4X4 under your drain hose to raise it up and create a water trap. The water trap will prevent any sewer gas from the park to enter your MH. However if you leave your valve open all the time, then Pure Power won't help since it will drain out right away.
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Old 10-20-2020, 09:50 PM   #5
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Also something to look at - your sinks and shower should all have functional traps, they MAY have located nearby on the pipe a spring-loaded vent cap INSIDE under the cabinets. That's likely where the smell is coming from. The idea with those is they are supposed to open inward to the pipe to prevent any suction in the pipe from draining the traps. From a practical perspective this rarely is a concern but the spring and rubber DOES wear out as these are really cheap things from the hardware store.

You may need to cut them off and replace them or (as I did) just replace with a solid cap and forget they exist. I have never had a problem with the traps being sucked dry, but I HAVE had problems with tank-stank coming in through these failed ports when the roof vent wasn't working properly! After capping the vents off internally and resolving the roof vent, no more smell.

Installed a couple of these on the two roof vents, and there hasn't been a whiff of smell since:

They are completely passive and work in the slightest breeze - just dig out the old cap until you can see the actual pipe, wipe a bit of silicone on the inside of this as an adhesive and glue it right to that pipe. Then seal the roof around the exterior. Problem solved.
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Old 10-20-2020, 10:29 PM   #6
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Don't put any food waste down the kitchen sink. I about got driven out one night in a 25 mile an hour wind straight from the rear. Changed my roof vent to a lippart 360 degree and I wipe my dishes clean before washing. No more problems. 4 lb box of borax , cup of dawn dishsoap and about 7 gallons of water with a 20 mile in town drive will clean it completely.
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Old 10-21-2020, 08:38 AM   #7
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Thank you all for the great suggestions. WIll implement them today. I am sure I will get this problem solved quickly now.
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Old 10-21-2020, 10:05 AM   #8
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Just saw this thread today, and will agree with those who said to close your dump valve.

As noted, the odor is from the entire park's sewer system, not just your grey tank. You, through your vent pipe, are essentially an open sewer connection, not unlike someone leaving the screw cap off of the dump port at a campsite. Yes, the grey tank alone can have foul odors, but not as foul as the entire septic system of a park.
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Old 10-21-2020, 11:23 AM   #9
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Form a "sag" in your sewer hose. That will act as a trap to separate your grey tank from the park sewer system. I use some wood blocks under the sewer hose to cause the hose to sag between the blocks. Due to the large diameter of the hose it takes about 6" of sag to create an effective trap.

Alternatively, close your grey tank dump valve and only open it to dump the grey tank.
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Old 10-21-2020, 12:22 PM   #10
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Gain fabric softener from the dollar store keeps things smelling good in ours. The green stuff like $4 a gallon
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Old 10-21-2020, 01:37 PM   #11
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Hi ! Welcome to IRV2! We're sure glad you joined us!

Happy Camper tank treatment will solve your problem!

Good luck, happy trails, and God bless!
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exhaust, gray tank, odor, tank

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