By what percentage should the size of a septic tank be increased if it has a garbage disposal unit?

When incorporating a garbage disposal unit into a septic system, the size of the septic tank should indeed be increased to accommodate the additional solids and organic material that the disposal unit introduces. A garbage disposal typically adds more waste to the system, which can increase the need for a larger tank in order to maintain proper treatment and prevent system failure.

Increasing the size by 50 percent is a widely accepted practice among professionals in the wastewater management field. This adjustment is meant to ensure that the septic tank can handle the increased load of organic material from food waste without risking the effectiveness of the treatment process. A septic system's primary function is to provide adequate detention time for solids to settle and for microorganisms to break down waste; thus, a significant increase in size helps achieve this balance, reducing the chances of backups and system overload.

In contrast to the other options, a 50 percent increase strikes a balance that is most beneficial for accommodating the extra waste without overly complicating the system or incurring unnecessary costs associated with significantly larger tanks.