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  1. #1
    Seasoned Camper
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    vent problem with shower/bathroom sink drain

    So twice now at or near the end of a shower in our 2022 378 MBS an air "bubble" has erupted from the bathroom sink drain. Then the shower continues to burp and gurgle as it finishes draining into the front gray tank. This is with the gray tank dump valve closed.....have not tested it with the dump valve open yet.
    I'm assuming there is a problem with a vent on this line? There is a vent/air valve above the level of the trap on the standpipe under the sink...wondering if that is the only vent for the shower and sink? Maybe it's stuck or bad?
    Its raining and cold here in Phoenix or I would go up top and check to see if a roof vent might be plugged, or if there even is a roof vent for the gray tank.
    Any thoughts?
    Thanks,
    SteveM
    2022 Solitude 378-MBS-R, 8k axles and disc brake package, slide toppers, dual panes, 5.5kw Onan, W/D, 3rd AC/heat pump
    2023 F350 Lariat DRW on order, (canceled)
    2023 Chevy 3500 LTZ long bed Duramax, 12250 GVWR, 3867 cargo cap, Z71, 5th wheel prep

  2. #2
    Long Hauler
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    Quote Originally Posted by smullinax View Post
    So twice now at or near the end of a shower in our 2022 378 MBS an air "bubble" has erupted from the bathroom sink drain. Then the shower continues to burp and gurgle as it finishes draining into the front gray tank. This is with the gray tank dump valve closed.....have not tested it with the dump valve open yet.
    I'm assuming there is a problem with a vent on this line? There is a vent/air valve above the level of the trap on the standpipe under the sink...wondering if that is the only vent for the shower and sink? Maybe it's stuck or bad?
    Its raining and cold here in Phoenix or I would go up top and check to see if a roof vent might be plugged, or if there even is a roof vent for the gray tank.
    Any thoughts?
    Thanks,
    SteveM
    Check the AAV (Air Admittance Valve) under the bathroom sink. That most likely is your culprit.
    Mark & Mary. Full-timing across the USA (and Canada)!
    Current Coach: 2021 Grand Design Reflection 320MKS
    Current Rig: 2019 Ford F350 SD Crew Cab, w/8' box, Lariat, SRW, 6.7l Diesel

  3. #3
    Seasoned Camper
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    Quote Originally Posted by MoonShadow_1911 View Post
    Check the AAV (Air Admittance Valve) under the bathroom sink. That most likely is your culprit.
    I'm thinking you are right. Any way to check or adjust it? Or just replace it......and are these valves a specialty RV item or the same as what I can pick up at Lowes/HD?
    2022 Solitude 378-MBS-R, 8k axles and disc brake package, slide toppers, dual panes, 5.5kw Onan, W/D, 3rd AC/heat pump
    2023 F350 Lariat DRW on order, (canceled)
    2023 Chevy 3500 LTZ long bed Duramax, 12250 GVWR, 3867 cargo cap, Z71, 5th wheel prep

  4. #4
    Site Sponsor
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    The air admittance valve is designed to let water in to break the vacuum in the drain line when you are using the sink. It should not allow air out (into the RV) or you would have some very foul odors in your camper. The burping you describe is probably from pressure buildup which is normally caused by a plugged tank vent which should have its opening on the roof. I have seen a lot of different reasons for a vent to not work properly from it being plugged, (which shouldn’t happen on a grey tank), to the vent being incorrectly installed so the top of it is covered, to sometimes the vent pipe not being properly secured and it has slid down into the grey tank so the bottom of the vent is below the level of the water in the tank. In other words, you have some detective work ahead of you to find the cause and fix it.
    2022 Reflection150 226RK
    2022 F150 Powerboost hybrid with 3.5L Ecoboost


  5. #5
    Long Hauler
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    Quote Originally Posted by smullinax View Post
    I'm thinking you are right. Any way to check or adjust it? Or just replace it......and are these valves a specialty RV item or the same as what I can pick up at Lowes/HD?
    It's a common plumbing part. You can replace it with one from any big box hardware store.

    Quote Originally Posted by DougW9876 View Post
    The air admittance valve is designed to let water in to break the vacuum in the drain line when you are using the sink. It should not allow air out (into the RV) or you would have some very foul odors in your camper. The burping you describe is probably from pressure buildup which is normally caused by a plugged tank vent which should have its opening on the roof. I have seen a lot of different reasons for a vent to not work properly from it being plugged, (which shouldn’t happen on a grey tank), to the vent being incorrectly installed so the top of it is covered, to sometimes the vent pipe not being properly secured and it has slid down into the grey tank so the bottom of the vent is below the level of the water in the tank. In other words, you have some detective work ahead of you to find the cause and fix it.
    You have a point here.
    @smullinax you might want to check the vent, first.
    Mark & Mary. Full-timing across the USA (and Canada)!
    Current Coach: 2021 Grand Design Reflection 320MKS
    Current Rig: 2019 Ford F350 SD Crew Cab, w/8' box, Lariat, SRW, 6.7l Diesel

  6. #6
    Seasoned Camper
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    So to follow up; after dumping tanks yesterday I left the forward (shower/bath sink/washer) gray tank valve open. Used the shower last night with no gurgling or slow draining at all. I also pulled the air admittance valve under the sink....nothing to see there, but I'll probably replace it just so I won't be thinking about it.
    So until I get up top to check for a possible blockage I'll just leave the front gray dump valve open. The 378 has 2 gray tanks, so I can hold water in the rear (kitchen sink) tank for flushing the sewer line..... maybe having the 2 gray tanks is a plus after all!
    Will be a couple of weeks before I can follow up...going over to CA to finish a remodel on an old beach trailer. Talk about a frustrating project! At least with an RV the original parts were made in this century.
    2022 Solitude 378-MBS-R, 8k axles and disc brake package, slide toppers, dual panes, 5.5kw Onan, W/D, 3rd AC/heat pump
    2023 F350 Lariat DRW on order, (canceled)
    2023 Chevy 3500 LTZ long bed Duramax, 12250 GVWR, 3867 cargo cap, Z71, 5th wheel prep

  7. #7
    Rolling Along
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    Suggest you close it when not using it so as too separate your systems from the sewer system. Generally a good idea.
    2021 Reflection 312 BHTS, Silverado 2500 Duramax

  8. #8
    Seasoned Camper
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    Quote Originally Posted by DougW9876 View Post
    The air admittance valve is designed to let water in to break the vacuum in the drain line when you are using the sink. It should not allow air out (into the RV) or you would have some very foul odors in your camper. The burping you describe is probably from pressure buildup which is normally caused by a plugged tank vent which should have its opening on the roof. I have seen a lot of different reasons for a vent to not work properly from it being plugged, (which shouldn’t happen on a grey tank), to the vent being incorrectly installed so the top of it is covered, to sometimes the vent pipe not being properly secured and it has slid down into the grey tank so the bottom of the vent is below the level of the water in the tank. In other words, you have some detective work ahead of you to find the cause and fix it.
    Sorry for the delayed response on this issue....so I changed out the AAV yesterday, but the shower still "burped" through the vanity drain at the end of my shower last night. That's with the front gray tank dump valve closed. Doesn't do it with the dump valve open. I think DougW is right and the vent stack is too low in the gray tank. Even with it being under warranty I'm not going to deal with that kind of a project......we don't dry camp enough to make it worth the hassles.
    By the way, GD customer service did send me a replacement AAV, but it was a female thread, even though the pic I sent them of the original one showed a male thread. No way I'm trying to cut/replace a piece of that standpipe under the vanity, so I just picked up one at Lowes with a male thread.
    2022 Solitude 378-MBS-R, 8k axles and disc brake package, slide toppers, dual panes, 5.5kw Onan, W/D, 3rd AC/heat pump
    2023 F350 Lariat DRW on order, (canceled)
    2023 Chevy 3500 LTZ long bed Duramax, 12250 GVWR, 3867 cargo cap, Z71, 5th wheel prep

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