Pumping out your septic tank is something that should be performed at least every third year to make sure your septic system is working at top performance. If you wait too long to perform a septic tank pump out, the tank might become too full and start releasing waste back up the plumbing. However, there are times and circumstances when you should not pump out your septic tank, regardless of how long it has been since you've done it.
If you are experiencing flooding of your property, you should avoid pumping out your septic tank. The reason for this is not in fear of the content of the septic tank leaking out into the flood water, but rather the opposite. If your septic tank is made from a heavy material like concrete, a pump out could allow flood water to enter the septic tank as the pipes are under water. This could significantly damage your septic tank by allowing harmful substances into it, which would demand some very extensive septic tank cleaning. If you own a septic tank built from a light material, such as fibre glass, the danger of a flood is that the water might lift the tank if it's empty.
Old and fragile septic tanks
If you are the owner of a very old septic tank, or if there's a septic tank on your property that is no longer in use, you should not try to pump it out yourself. You risk the tank breaking as you pump its contents out. A really old and fragile septic tank might have adapted to its content and will cave in when you remove it. Use the help of a professional to empty tanks like these, as they have knowledge on how to do it safely or from afar.
If you're having your septic tank inspected, you should abstain from pumping it out. The test won't be able to be performed correctly and may give misleading results. This is especially important if you're selling your house, as the new owners will want to have an inspection of their septic tank performed. Emptying the septic tank will not give them a complete result of the actual conditions of the house. If you are buying a house with a septic tank, you should, for the same reason, ask to have an inspection performed before you decide if you want to buy the house or not. Ask the owner specifically not do a septic tank pump out until you have gotten the inspection made.