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  1. #1
    Setting Up Camp StillCamping's Avatar
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    Grey tank question

    Hello everyone,

    My wife and I are the new owners (can’t decide weather it’s a good experience yet) of a 2019 grand design solitude 3350RL.

    We have two grey tanks. 50ish gallons each. The sink goes to one of them. And literally everything else goes to the other. When you enjoy your long showers and use a washer dryer unit it tends to fill up fast.

    I have done what everyone else has done and put a valve on the discharge pipe and left both grey valves open hoping the tanks will equalize. So far, no, they have not. I opened up the wall in the storage bay to actually see the tanks. I have a black and grey tank right next to each other, and another grey tank ABOVE both of them.

    The highest grey tank is for the sink, because why wouldn’t it be.. and the grey tank for the shower, and the washer is on the bottom. Since the bottom tank will always fill first for us, will it eventually back fill into the tank above it? I have not Filled the tank completely to find out for fear that water will back up into our closet (where the washer is)

    Anyone else have experience with this?

  2. #2
    Setting Up Camp StillCamping's Avatar
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    Racking my head on this one more than I should. The obvious answer to me is that no, they won’t ever equalize evenly. This all reminds me of those mechanical aptitude tests.. the only options I can think of is to redo the plumbing so the shower and washer discharge into the above tank FIRST and then drain into the bottom tank. Or keep both tanks independent of one another and plumb in some kind of transfer pump when the bottom tank gets full.

  3. #3
    Big Traveler Calbar's Avatar
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    Quote Originally Posted by StillCamping View Post
    Hello everyone,

    My wife and I are the new owners (can’t decide weather it’s a good experience yet) of a 2019 grand design solitude 3350RL.

    We have two grey tanks. 50ish gallons each. The sink goes to one of them. And literally everything else goes to the other. When you enjoy your long showers and use a washer dryer unit it tends to fill up fast.

    I have done what everyone else has done and put a valve on the discharge pipe and left both grey valves open hoping the tanks will equalize. So far, no, they have not. I opened up the wall in the storage bay to actually see the tanks. I have a black and grey tank right next to each other, and another grey tank ABOVE both of them.

    The highest grey tank is for the sink, because why wouldn’t it be.. and the grey tank for the shower, and the washer is on the bottom. Since the bottom tank will always fill first for us, will it eventually back fill into the tank above it? I have not Filled the tank completely to find out for fear that water will back up into our closet (where the washer is)

    Anyone else have experience with this?
    They will never equalize if one tank is above the other. The kitchen sink tank should stay empty until the other tank fills up and then the kitchen sink should fill up. All assuming that both tanks drain through the same outlet and a plumbed together.

    Rob
    Rob & Barb
    2022 Solitude 378MBS
    2022 RAM 3500 SRW HO Aisin 4x4
    Waterloo, Ontario, Canada

  4. #4
    Rolling Along RVRunners's Avatar
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    I keep a valve on the outlet as you describe and keep both grey tank valves open. Not sure if the tanks are level with one another but this approach will work to give you some more capacity. Those who previously posted are correct that the tanks will only equalize if they are level with one another.
    The Adams - 2017 Reflection 367BHS, 2019 F-350 6.7L PSD 4x4 CC DRW, B&W hitch on Ford pucks, Air Lift Loadlifter 5000 Ultimate Plus air bags, "Rupert" the Weimaraner.

  5. #5
    Setting Up Camp StillCamping's Avatar
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    Lol. Yep. I think I’m gonna re route the plumbing to hit the highest grey tank first. That way it should all flow down without anything being able to back up.

  6. #6
    Rolling Along jim1521's Avatar
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    As long as you have good P-traps you can just leave the gray tanks open and let them dump into the sewer. I also create a P-trap in my sewer hose as well to keep a vapor barrier between the tanks and the sewer.
    2016 Grand Design Reflection 313RLTS
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  7. #7
    Setting Up Camp StillCamping's Avatar
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    The camp ground we spend the summer at doesn’t have full hookups. So we need to wheel our waste to the dump station.

  8. #8
    Site Team traveldawg's Avatar
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    Quote Originally Posted by jim1521 View Post
    As long as you have good P-traps you can just leave the gray tanks open and let them dump into the sewer. I also create a P-trap in my sewer hose as well to keep a vapor barrier between the tanks and the sewer.
    It's been my experience that if leaving the valves open all the time solids will build up in the tanks and the discharge plumbing. When you think about it, solids & heavy stuff always sinks. And with the waste gates open you just can't get enough water flow to flush things that settle to the bottom out. Yes, there are solids in grey water waste - bits of soap, bits of sink garbage, grease from washing dishes (even when using a screen type striker, tooth paste particles - whatever.

    I learned this after being in place in one location for an extended stay. When I finally pulled the sewer hose off to relocate to another location I couldn't believe the build-up in the drain pipe. Soap gunk, bits of food particles (even tho we use strainers) - yuk.

    I think the better advice is to let the tanks get some good amount of water in them (just like the advice for the black tank) and then drain.

    About trying to expand the capacity of the lower tank - I don't think that's going to happen. But you can always install a lift pump to move water around.
    Larry KE4DMG
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    2019 310GK-R - Sailuns; MorRyde IS; Disc Brakes; 20K Reese Goosebox
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  9. #9
    Rolling Along
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    Quote Originally Posted by jim1521 View Post
    As long as you have good P-traps you can just leave the gray tanks open and let them dump into the sewer. I also create a P-trap in my sewer hose as well to keep a vapor barrier between the tanks and the sewer.
    Also leaving your tanks open all the time might allow ‘critters’ to get in!

  10. #10
    Big Traveler boyscout's Avatar
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    Quote Originally Posted by jim1521 View Post
    As long as you have good P-traps you can just leave the gray tanks open and let them dump into the sewer. I also create a P-trap in my sewer hose as well to keep a vapor barrier between the tanks and the sewer.
    @StillCamping @traveldawg beat me to it but just to reinforce his point, where RV tanks are concerned water is your friend. Letting the tanks fill up reduces the chance that bits of food, soap films and oils, and other things that get into the drain won't stay in the tank and solidify there, eventually likely interfering with outflow.

    There are videos on YouTube in which someone has simulated tanks with clear Lexan-like material and demonstrated the difference between having a lot of water in the tank and having little (or no) water in it. Lots of water means when dumping it lots of the stuff in the tank goes out the outflow, otherwise it stays in the tank. Even when dumping with lots of water, a surprising amount of stuff stays in the tank, which is why its also a good idea to run a few gallons into the tank after dumping it so it will be less likely to solidify.

    A p-trap is only going to "trap" a small portion of the solids and oils, and only until the next time water is run through it. It's always best to prevent these things from even getting into the p-trap, and there are drain screens available to help with the solids part of that. But it's inevitable that stuff gets in so long-term, letting the tanks fill and occasionally using the "GEO method" or some of the commercially-available products for keeping tanks clean will reduce the risk of really messy troubles down the road.
    Mark - 2018 Solitude 310GK - 2017 F-350 diesel SRW short box - Pullrite Superglide hitch

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