Kitchen greywater with food solids and fats will quickly impair a tiny house septic system so a simple pre-treatment grease trap and solids removal strategy is essential.

For a tiny house install a small grease trap or interceptor sized for low flow, typically from two to five gallon capacity for most single kitchen setups, and position it upstream of the septic tank so oils and floatable fats separate before entering the drainfield. Use a mesh or settling basket in sink drains to capture large food particles and keep a removable baffle in the trap to slow flow and improve separation. If you have a separate dishwasher check local codes and septic capacity and only route that discharge to sewer when allowed because dishwashers can flush fine solids and detergents that re-suspend settled grease. Avoid using a garbage disposer because shredding food increases the load of organic solids and accelerates clogging; instead collect food scraps in a sealed countertop container and compost them off-system or use municipal organics where available. Establish a cleaning schedule based on use, for example inspect weekly for trapped solids and perform a full trap clean every one to three months depending on meal volume, and always wear gloves and follow safe disposal practices for removed grease and solids by sealing them in a nonpermeable container for landfill or approved waste hauling. Use enzyme or bacterial additives only as an adjunct to mechanical separation, not as a replacement, because they cannot remove free oils and solids and may simply move organics into the septic tank without reducing hydraulic or grease load.

The most common mistake is undersizing the interceptor which causes frequent carryover of grease into the septic tank; size to expected peak kitchen flow and choose the larger option when in doubt and add baffles to slow flow. People often rely solely on chemical treatments or enzymes which do not remove macro solids and fats that accumulate; use mechanical capture like baskets and periodic physical clean-outs to prevent build up. Another frequent issue is routing all greywater, including dishwasher and laundry, into the tiny system without accounting for detergent and solids impacts; where local rules permit route dishwasher separately or increase pretreatment capacity and avoid disposers so the primary separation can function as intended.

We at BigHomeProjects.com help homeowners find local contractors who can size and install small grease interceptors and advise on code compliant routing for tiny house systems. Our site also helps contractors find work and join an active discussion community where we and other members share practical tips, schedules, and local code experiences.

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