This question is asked more often than you'd think
Even though the answer is simple in theory, it opens up a conversation about how your system works, how you can save money on pumping, and how often you should schedule your maintenance. We have articles covering these other topics in detail, so for now let's focus on how to determine how full your tank is.
If you were to pop the lid on your tank right now, you should see that the fluid level is pretty high, generally 6-8inches from the lid. Under normal use, your tank should completely fill with fluid in 4-7 days. Some people are concerned when they see how “full” a tank is even when it's mostly liquid, and that's why we use the “scum level” method.
The reason your tank needs to be serviced is because of the solids content. Over time, solids build up in your tank that can't effectively be eaten by microbes and transported to your soil treatment area (STA) or lagoon. All these solids build up and when they reach roughly one third of the volume of the tank, the efficiency of the microbes breaking down solids lowers substantially and the effluent retention time goes down and serious damage can be done to your STA! So, how do I know how full of solids my tank is?
Scum level, it's about as gross as it sounds. Outside of buying special equipment, taking a shovel and testing the depth of the top scum layer is as close as you're going to get. A good general rule of thumb is for every inch of scum floating on the top, there's at least one half of an inch of sludge on the bottom of the tank. These two measurements combined should not be more than one third of the liquid depth of your tank! This method, in my experience, isn't very reliable, at least in our region surrounding Durango, CO. Salt water softeners, some detergents, vacation homes and rentals often produce much different results, this is why we recommend pumping on a 3-5 year basis for most residential applications.
For more information on Mountain Septic and our septic aerator repair services, feel free to reach us via phone today: (970) 238-7884.