Septic tank filters are designed to keep solid particles in the septic tank. They are located on the outlet side of the tank where the tee is normally placed. Some filters fit inside the tee and some replace the tee. There are several different filter designs for residential applications and also for commercial use. Most residential filters trap particles larger than 1/16 to 3/16 of an inch in size. These photos show a filter that has been in operation at a trailer park. Yes, taking this photo was a yucky task but the filter was doing its intended job. By trapping solids, the filter protects all downstream components, like the pump and drainfield, from damage. This filter, like all we know of, can be cleaned and returned to service.
Virginia doesn't require homeowners to have a filter on their septic septic tank. All the same, it's not a bad idea to do. In theory, and as near as we know now, in fact, these filters clog at about the same rate as a tank needs to be pumped out. The advice to pump out a tank every 3 to 5 years is pretty much conservative average advice. Some people need to pump their tank more frequently and some people can increase the interval. Rather than just forget about your tank, which is easy to do, the filter can be used to remind you that it's time to pump your tank. Most residential filters cost less than $100 and are easy to install when the system is new or when you have it pumped out. Compared to the cost of replacing a drainfield, this is cheap insurance.
When was the last time you pumped your septic tank? You know, now might be a pretty good time to have done.