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  • Black water tank dimensions

    We have a 2021 transcend 221rb. Does anyone know how deep the bw tank is? My inlet pipe from the toilet is 3.5 to 4 inches from the bottom of the tank. Once it is 1/3 full everything solid has to sit in the pipe, paper etc does not sink. I would think the pipe should be at 8" from the bottom of tank.
    2021 Grand Design Transcend 221RB
    2018 f150 4x4

  • #2
    howson @Cate&Rob, Can either of you confirm if this is the correct tank? https://www.granddesignrv.com/owner-...s/detail/48846

    based on the drawing the tank tapers from 6" to 8".
    Joseph
    Tow
    Vehicle: 2024 GMC K3500 Denali Ultimate Diesel
    Coach: 303RLS Delivered March 5, 2021
    South of Houston Texas

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    • #3
      Is that the only tank they use? I dont see on the diagram how far in the inlet pipe should go. It is a 2021 Grand Design Transcend 221RB
      Vin - 573TT2723M8815719
      2021 Grand Design Transcend 221RB
      2018 f150 4x4

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      • #4
        No clue. I do not have access to that information. Howson or cate&rob ma have the information.
        Joseph
        Tow
        Vehicle: 2024 GMC K3500 Denali Ultimate Diesel
        Coach: 303RLS Delivered March 5, 2021
        South of Houston Texas

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        • #5
          Mokey Jlawles2

          All holding tanks are in the range of 6" to 8" deep (per the drawing that Joseph linked) because of the available space under the floor. The drain (and vent) pipes entering the tank should sit in rubber grommets which extend only about 1" into the tank. It is possible and has been reported/discussed here before that sometimes a pipe gets pushed too far through the grommet during production, which can reduce the available volume of the tank as you describe. This more often occurs when the vent pipe is pushed too far into the tank because as soon as the liquid level covers the end of the vent pipe, air cannot be displaced to allow more liquid in.

          It would seem that the pipe (or pipes) going into your tank need to be shortened. Sometimes the grommet can be reused, but to be sure of a good seal, it should probably be replaced at the same time.

          Rob
          Last edited by Cate&Rob; 07-07-2021, 06:48 AM.
          Cate & Rob
          (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
          2015 Reflection 303RLS
          2022 F350 Diesel CC SB SRW Lariat
          Bayham, Ontario, Canada

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          • #6
            Originally posted by Mokey View Post
            Is that the only tank they use? I dont see on the diagram how far in the inlet pipe should go. It is a 2021 Grand Design Transcend 221RB
            Vin - 573TT2723M8815719
            The Ht1024 is what I have, too (39 gallon). Same tank for rear grey. Water is a 56 gallon, front grey 29 gallon.

            Substitutions very possible--only GDCS will know for sure by consulting the build sheet.

            I do not know vent criteria for any tank (sorry).
            Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

            2017 Ford F-350 DRW, '19 315RLTSPlus

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            • #7
              I would expect the inlet pipe to enter very little, if at all.
              Ted
              2021 Reflection 310RLS
              2020 F350 PS,CC,LB,SRW

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              • #8
                In the attached picture, you can see the outer "slot" where the grommet fits to the tank top and the inner "ridge" at the bottom that is suppose to stop the pipe from going in any further. It is not difficult to push the pipe past this ridge during installation. If the pipe stops at this ridge, it will only be about 1/2" into the tank.

                Rob

                Click image for larger version

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                Cate & Rob
                (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
                2015 Reflection 303RLS
                2022 F350 Diesel CC SB SRW Lariat
                Bayham, Ontario, Canada

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                • #9
                  Contact Grand Design with your VIN and they will send you the specs for your exact tank.
                  Worked for me
                  -
                  Rob, Chris and fur baby Maya
                  2019 Solitude 374TH, Victron Multiplus II 3000 2x120, 600AH of Battle Born LiFePO4, 1800W Solar, Blue Sky CC's, Starlink
                  2023 GMC Denali Duramax 4x4 DRW LB CC, Curt Q25
                  Follow us at https://rctravels.rmcd.ca/

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                  • #10
                    Originally posted by KamFlyer View Post
                    Contact Grand Design with your VIN and they will send you the specs for your exact tank.
                    Worked for me
                    Grand Design has already posted the drawing of this tank in their parts list. See the link in post 2.

                    Rob
                    Cate & Rob
                    (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
                    2015 Reflection 303RLS
                    2022 F350 Diesel CC SB SRW Lariat
                    Bayham, Ontario, Canada

                    Comment

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