A holding tank is used for an onsite system that has no soil component for a variety of reasons (small lot, lake lot, no suitable soil, etc.). Holding tanks have to be pumped regularly. Because every gallon of water that goes in must be pumped out, the homeowner is typically quite sensitive to anything that causes the tank to fill up faster and cause the need to be pumped more frequently.
When troubleshooting tanks (whether holding or septic tanks) that are filling up “too fast,” check some of these possible causes:
1. Clear water sump pump: This is the sump pump that picks up draintile water from around the foundation. This should absolutely not be going to a holding tank (or septic tank). Clear water sump pumps typically pump outside the foundation, many times to the ground surface and in some cases subsurface. It’s just pumping clean groundwater away from the building. This will fill tanks way too fast, causing frequent pumping — and in the case of an onsite system, hydraulic overload and premature failure.
2. Sanitary sump pump: The sanitary sump pump in a basement is designed to be pumping to the holding tank (or septic tank). It basically lifts any basement level (or lowest level) water up to the shallower sanitary sewer pipe so tanks don’t have to be 9 feet deep in the ground. The sanitary sump pump typically pumps water from a floor drain, laundry tub — whatever plumbing is in the basement or subsurface level of the house. The sanitary sump pump should not be picking up draintile or groundwater. Sanitary sump pumps are installed in the basement floor to pick up the lowest plumbing. That also makes them susceptible to errantly picking up and pumping groundwater to the holding tank if the sump crock is compromised (not watertight) in any way. Older sanitary sump crocks used to be concrete and in many cases lose watertightness over time, filling with groundwater if in a high groundwater location. Make certain the sanitary sump crock is only pumping the water from the plumbing fixtures it should be, and that it is not picking up groundwater.
Please also note that the pipes beneath the basement floor that are supposed to go to the sanitary crock could be compromised and picking up groundwater from beneath the floor on the way to the sanitary sump crock. This is easily found by pumping down the sanitary crock and watching the few incoming pipes. If you aren’t using water in the basement, but water is flowing from the pipes into the sump crock, they could be picking up groundwater, and that groundwater is being pumped to the tank.
3. Silent toilet leaks: Have customers do the dye test. Put food coloring in the tank and do not flush. If the color shows up in the bowl, the toilet is adding a lot of nonstop extra water to the system's flow. This is a really big issue. I did troubleshooting for a very busy commercial establishment, a bar/restaurant on a major highway. The bar’s holding tanks were always full. Troubleshooting of the establishment easily determined that one really badly leaking toilet was quickly filling large commercial holding tanks. Do not underestimate this source of water.
4. No basement: If a house or other building on a holding tank does not have a basement, pipes beneath the floor could be picking up groundwater from beneath the building and filling the holding tank with clear groundwater that should not be going to the holding tank. Underfloor plumbing might require lining or replacement. Pump the tank and make sure no water is being used in the house. Watch the inlet pipe closely for any water coming in.
5. Water softener/iron filter: Recently we evaluated an onsite system for a home sale and the house was vacant. With proper protocol, we pumped the tank(s) to evaluate their condition. Two days later I stopped by to check something. I opened the tank and it was filled with crystal clear water. While looking in the tank I heard more water pump into the tank. The house was vacant, so there was no water being used. I checked all of the possibilities listed above. Turns out the water softener and iron filter recharges were pumping directly into the tank and obviously had some sort of issue because they filled the tank in two days. I would recommend that water softener/iron filter recharges not go to any type of onsite system. I always recommend they be pumped to the clearwater crock or directly out of doors when and where allowed. This is clean enough water that does not have to be treated so there is no reason for this water to be filling the onsite system tank(s).
6. Infiltration: Is the water getting into the tank from surface stormwater? Is the tank cover flush at grade? Does the grade flow toward the manhole cover? When possible, manhole covers should be a minimum of 4 inches above grade in a yard. The grade should pitch away from the cover, not toward it. Recently while troubleshooting a holding tank filling up too fast, we discovered a grade that floods out so high during rains, the water flows in through the electrical hole in the riser into the tank (see picture). Also look for downspout extensions emptying too close to manhole covers.
7. Tank inspection: The other obvious place to look for water infiltration is through the tank itself. Are there cracks? Is the seal around the pipe leaking? Pump the tank and safely use mirrors and spotlights, a cellphone with flash, or other means of safely inspecting the interior of the tank without entering the tank. If you do have to ever enter a tank, only do so with OSHA-certified confined-space entry trained personnel and the proper equipment. My company’s policy is to attempt every other means possible before bidding tank entry. I just watched some videos taken by someone evaluating a tank, and the cracks weren’t even visible, but the water rushing into the tank sure was. In older tanks it’s sometimes very difficult to see the condition due to age, construction material, and solids buildup inside. Often the leaks into the tank are obvious; many times they are much harder to see.
8. Alarm float switch: Another recent issue was when a customer said that all of a sudden their tank filled up faster and they were pumping more frequently; so they were convinced there must be a leak. Thorough evaluation determined their alarm float merely slid much lower, activating the alarm more frequently. Pumping records showed that fewer gallons were being pumped each time, corroborating our findings. All that had to be done here was to adjust the level of the alarm float switch, and they were back to their typical pumping frequency.
There could be other ways not listed here but these seem to be some of the major ways tanks fill up faster with extra water. I hope the above helps in thinking of ways "extra" water might be making it into a tank. Good luck troubleshooting, and stay safe!
About the author
Todd Stair is vice president of Herr Construction, Inc., with 34 years’ experience designing, installing, repairing, replacing and evaluating septic and mound systems in southeast Wisconsin. He is the author of The Book on Septics and Mounds and a former president of the Wisconsin Onsite Water Recycling Association.
