It's natural to think that a clean septic tank is best when you're about to have the tank inspected. The tank would be empty, the inspector could see how clean it was, and you could get an idea of what the full capacity of the tank would really be like, right?
On the contrary, you shouldn't pump it out just before an inspection. An inspection takes place for specific reasons. Maybe you're about to sell the house, or there have been complaints about the tank or the drains in your house. That means that the inspection needs to include proof that the tank is working fine when it is holding solids. And that means that you should not empty out the tank, lest you be accused of fraud.
A common test for a septic system during an inspection is a dye test. A liquid dye is placed in the system to check for leaks and backups. If the tank is emptied out first, the dye won't go anywhere and will only show if there is a leak at the very bottom of the tank. So if there's a leak around a pipe connection, for example, or toward the middle of one side of the tank, you won't know because the dye won't be able to reach those points.
That Fraud Thing
Because dye tests and inspections are often done before a home sale, making it harder to see if something is wrong with the tank is not good. In fact, if it turns out there is something wrong with the tank and you prevented the buyer from finding out because you had the tank pumped out first, they could accuse you of knowingly making it impossible to test the tank properly.
Even if you did not know you were doing something wrong, that can create a lot of legal trouble for you, to put it mildly.
If It's Truly Time to Empty the Tank
So what do you do if you neglected to empty the tank on its usual schedule, and you really need to have the thing pumped so that your drains keep working -- but you've got an inspection scheduled? In that case, contact the inspection company and let them know what's going on and why you really need to get the tank pumped out. They may be able to arrange a test very quickly, so they can get the results they need without delaying you further. Or, you can push the test out, and the inspectors will let you know how much time needs to pass between the cleaning and the test.
If you've already cleaned out the tank, call the inspection company immediately and let them know. They know that not everyone realizes that cleaning out the tank before an inspection is bad, and they'll work out a different schedule with you. Companies like Linn Septic Service can help with your cleaning and inspection needs.