How to avoid holding tank problems

We replaced more holding tanks last year than we would have liked to.  It’s a costly and messy repair. We want to help you learn more about your RV so that you can try to avoid it: Excel uses 2 piece holding tanks that are parallel to the RV under the basement. Excel made a frame from 2X2s, angle iron, and a cross member for the wider lip of the holding tank to rest upon. Most of your tanks are hanging down suspended from the frame.  When the weight of the waste accumulates in the body of the tank, it applies an extraordinary amount of pressure to the seam where the tank and the lip meet.   A majority of the tanks that fail will have stress cracks along the weakest point in the seam along that lip. To avoid splitting your tank, haul with a minimal amount of fluid/ weight whenever possible. If your tank is fuller, try to drive slower to prevent the waste from moving as much. Additionally, your tank sensors are good indicators to watch, however, keep in mind that they simply report if fluid has reached the point that they were mounted on your tank.  Typically, your tank has almost two more inches above that full mark sensor. Some of our customers try to fill every inch– please don’t do this! Too much weight and pressure causes cracks, and filling your tank completely full leaves no room to relieve pressure from movement and your tanks will crack.

Some of the newer Excels came with extra straps underneath of the holding tanks to support the tanks when they are fuller, and we have seen some customers who added more support. These are great supplements, but we still see the tanks split at that top lip because of the pressure from hauling with too much liquid in the tanks.

If you are using your tank flush and close your valves, you run the risk of it overfilling.  When you over fill the tank, if you are lucky the waste will travel up the vent pipe and make a mess on your roof, or over flow through your toilet and flood your bathroom. If you’re unlucky, it could burst your tank. If you are cautious and follow these recommendations, there is a good chance that you can prevent the costly and messy problem of cracked or burst holding tanks. As always, give us a call if you have any questions or concerns, and call us as soon as possible if you notice a leak!



  • Larry Rosenow says:

    Hi. I have created a holding tank problem, I think, on my Excel 33RKO. My black tank valve wouldnt entirely shut so I let it leak into a 5 gal plastic bucket which I emptied faithfully into my residential sewer access pipe alongside my house. My friends who stay there primarily use gray water which I forgot to drain before leaving on a 6 wk vacation. When I returned the underbelly cloth was leaking grey water. So I backflushed the black tank, got interrupted, and didnt return until black water was leaking out of the bellycloth. Ug. So I opened up to expose part of the tanks and shut-off valves and removed all the soiled wet insulation. Unsure what the damage is; my request “where do I go from here?”

    • kathy says:

      It sounds like you’ve overfilled the black tank when you flushed it: if you flushed it with water straight from a spigot, the gallons per minute fill rate (from a spigot) means that the tank fills faster than it can flush out of the drain valve. If a tank is over filled, it can balloon out and break, thus leaking out the underbelly as you’ve described. Frequently, a black tank will split at the top where the 3” toilet pipe is plumbed into the tank. There is a collar around the plumbing join, which is too inflexible to allow flexion when the tank balloons, so an overfilled tank will crack around the bottom of that collar. Another common place for a tank to split is along the seam where the top and bottom of the tank is joined: this is hard to check as you can’t see the seam while the tank is inside the trailer. Cracks can also happen in other areas as well—these two places are just the most common. If you don’t see cracks or other evidence of leaks (like calcium build up) around the collar, leave the access panel down so you can see the tank, hook up the sewer flush and look for leaks on the tank itself. Keep track of about how much water goes into the tank before you see a leak so that you know about how much you can fill the tank before it leaks.
      The grey water tank sounds split too—especially if it was full when you moved it. If you have a washing machine in your RV, the gallons per minute flow rate from your washing machine is about the same as from a water spigot, so it is easy to overfill your grey tank in a hurry with your washing machine. You can do the same procedure to check for leaks on your grey tank as you do on your black tank.
      Ultimately, it sounds like you will need to replace your tanks. Sorry about that.

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