YES, In times of heavy rainfall your septic tank can behave as if it were full and needs to be pumped out.
If a heavy rainfall, or any other source of water such as draining a swimming pool or when a sprinkler hose is left on for an extended period of time, the drain field area connected to a septic tank can saturate and the tank will not be able to drain properly.
You may experience slow drains or water might even back up into your drains causing you to believe you have a clog. If using a septic safe chemical drain opener or plumbing snake fails to solve the problem, you may assume the septic tank is full. However, this may or may not be the case.
Opening the tank cover and visually inspecting the tank will tell you if the tank needs pumping. If it is half full with solids pumping it out gives you extra space for processing. Pumping a septic tank that is simply flooded with water will not solve the problem if the source of the flood continues. It will simply fill back up again. In addition, pumping a flooded septic tank can cause serious damage to the tank because the water pressure on the outside of the tank becomes greater than inside the tank due to the flooded soil.
A septic tank drain field is much like a drip irrigation system. It's a series of perforated pipes which allow the waste water to slowly drip out into the ground. The pipes are buried underground and surrounded with gravel. The old saying "the grass is always greener over the septic tank" is not entirely true, it's actually greener over the drainfield.
The septic tank itself is an enclosure with a pipe leading in from the house and another leading out into the drain field. The main drain pipe branches off into several pipes like a giant fork. Wastewater seeps out of the perforated drain pipes into the surrounding dirt where soil microbes clean the wastewater. Solids are left in the septic tank which is why they eventually need to be pumped out.
Think of it this way: If you were to hold one end of a pipe underwater and then try to run a hose into the other end, the pipe would simply fill up. This is how a flooded drain field can cause a problem. The waste water has nowhere to go but back up through the pipes.
Your best course of action for a flooded septic tank is to drastically reduce your use of water in the house. Don't flush the toilet unless absolutely necessary. If you can skip taking a shower, do so. Don't run the dishwasher. Try to dirty as few dishes as possible. You may even want to take your laundry to the laundromat or delay it a few days. If you have a pump, turn it off. In severe situations you may need to set up a portable toilet such as what you find on construction sites and fairgrounds. You need to reduce or eliminate water going down the drains until the drainfield dries out.
The most important thing to remember is: If the water isn't draining, don't put more in! You may need to progress through a number of steps to determine that your septic tank is simply flooded. If a plumber cannot clear the drain and has determined that the tank is not full of solid waste, he may need to run a camera down into the pipes to find out if the pipe is damaged, overgrown with tree roots or has simply collapsed. Old cast iron pipes eventually corrode and collapse and parking on top of the septic tank can also cause it to collapse.
There is no easy way to diagnose a flooded septic tank except by process of elimination and possibly a visual inspection of the inside of the tank itself. A non-working septic system is a serious issue.