Your garbage disposal will only affect the health of your septic tank if you’re using it too frequently, or filling it with organic waste that doesn’t fully break down. If the tank fills up with too many solids, the bacteria won’t have enough time to consume it before more is added, which can lead to an overflow in the drain field. Your tank will need to be pumped more frequently with excessive or improper garbage disposal use.

Replacing a garbage disposal costs anywhere from $150 to $950, but the average cost is somewhere around $550. There are two types of garbage disposal units, and continuous feed disposals tend to cost more than batch feed disposals. Going for an aluminum garbage disposal is also significantly cheaper than choosing a stainless steel garbage disposal. You'll also need to factor in the horsepower of the motor, labor, and the removal and disposal of your old unit.

Garbage disposals are durable appliances that usually last at least eight years as long as you clean and maintain them. It’s relatively rare for a garbage disposal to break on its own, as most malfunctions happen due to user errors, like overstuffing the grinding compartment or damaging the blades by trying to dispose of metal or bone. Eventually, cracks or leaks could develop in the unit, which requires a full replacement. 

These appliances certainly increase the number of things allowed down the drain, but they’re not foolproof. There are several items you shouldn’t put in your garbage disposal, according to manufacturers and technicians. Don’t put coffee grounds down the drain. The same goes for eggshells, potato peels, hard foods, onion skins, and any dry, expandable food. Most importantly, never put grease or oils down the drain.