Gravel Box filter replaced with in tank filter

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    • #279110

      Can I replace a gravel filter box with a zabel effluent filter in my tank?

      I have a typical “gravity feed type system”, with a 1000 gallon tank. The tank empties into a 2′ 3′ gravel filter box that was required by code when it was installed about 12 years ago. It goes from the filter box to the distribution box and out into the leach field. The leach bed is natural sand as far as you can dig, and percs very well.

      Originally, the filter box contained pea gravel. It plugged up after a while, so I dug it up and replaced the stone with some coarser crushed stone. I am going to get the tank pumped and will be installing a Zabel A1807-4X22 effluent filter in the cast in concrete baffle in the tank. Is the Zabel filter efficient enough to replace the function of the filter box – In other words, can I just remove the stone from the box and rely on the in tank filter to protect my field? I believe that the in tank filters are the only thing that is spec’d now – no more filter boxes. By the way, I will also be installing access risers and lids to grade to allow for ease of filter access. I want to be able to sleep at night…..and I never want to have to dig up that stinkin box and shovel nasty stone again!!!!!

    • #300070
      John Aldrich1

      Jim Bic, I believe that a new septic tank effluent filter is superior in functionality to the gravel box arrangement that you have described and currently curse. The modern filters are a lot easier to clean and maintain.

      There are other effluent filters on the market. I am particularly impressed with the Polylok PL-122 filter, available from Polylok, Inc. ( Polylok also makes an excellent riser and lid assembly for the septic tank risers. Another excellent effluent filter is made by the Tuf-Tite Company (

      » This message has been edited by John Aldrich on 25 October 2002

    • #300071
      Ken Zoeller

      Go to to see a filter in a filter made by Zoeller Co. All of the filters on the market plug up and need service. If they did not, they would not be doing their job. When a filter is lifted, a column of water is lifted on the clean side, opposite the dirt. When this happens the dirt is flushed off in the water and a flow event starts. When the filter is removed, all filters that I know of allow the flushed off dirt to pass to the next chamber.(Including the Poly-Loc, the red ball does NOT stop the flow only slows it down) Even the Zoeller’s primary filter does this(flushes off). However the Zoeller filter has a secondary filter that stays in place while the flow event happens, keeping the fallen dirt in the tank. While the flow event happens the primary filter is cleaned, when the flow event stops, the secondary filter can be hosed off in place or removed for cleaning. Please consider replacing the concrete baffle with a 4” PVC pipe, if it has any acid burns at all. It will not seal well to the gasket on the Zabel product. The Zoeller’s filter has 2 the filter area and it is 100% below the outlet vs the 1800 unit you are considering PLUS the secondary filter for protection when you clean it.

      » This message has been edited by Ken Zoeller on 25 October 2002

    • #300072

      Thanks for the input guys. I ended up using the zabel filter as it fit right into my concrete baffle in the tank. I also left the stone in the gravel filter box – the new guy that I had pump the tank out also cleans the gravel filter box out at no additional charge!!!! I will treat the zabel as a primary filter to be cleaned periodically and the gravel filter box will be a secondary protection against the flow events that occur when cleaning the filter. I also plan to block off the tank outlet when removing the zabel filter to avoid any solids from exiting, but even if they do, the gravel box will catch them.

      Thanks again for the advice.

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