**Connecting the laundry and sinks to your septic system can be a sound solution—but only if the tank and leach field can handle the added flow.** Septic systems commonly receive those wastes. Your concern is valid because your existing system has been operating with that water diverted elsewhere.

The main long-term risk is **overloading the leach field**. Extra water can saturate it, and large surges through the tank can carry solids into the field, contributing to clogging. A system working well under its current load does not prove it has spare capacity. [EPA guidance](https://www.epa.gov/septic/frequent-questions-septic-systems)

Here’s how I’d evaluate the options:

- **Connect to septic:** Investigate this first. Have a qualified septic designer or inspector review the original permit, tank size, field size and condition, household occupancy, and estimated added water use. Ask whether the system was originally designed for *all* household wastewater, and why the graywater was separated. The proposed connection should route wastewater through the septic tank before the leach field.
- **Install a new drywell:** Potentially reasonable if locally permitted and the new site has suitable soil and groundwater clearance. First confirm why the existing one stopped draining—a blocked pipe, accumulated material, and saturated surrounding soil call for different remedies. Replacing it without identifying the cause could repeat the problem.
- **Overflow pipe over the hill:** If this means dumping untreated wastewater onto the ground, I would avoid it. Sink and laundry wastewater can carry contaminants; moving the outlet downhill does not provide treatment. An approved subsurface graywater dispersal system would be a different proposal. [EPA explanation of wastewater and surface-water contamination](https://www.epa.gov/septic/septic-systems-and-surface-water)

Before spending the $3,000 or $5,000, I’d get the septic capacity assessment and check acceptable options with your local health/environmental department. In the U.S., those authorities generally maintain permit records and regulate modifications. [EPA permit and inspection guidance](https://www.epa.gov/septic/frequent-questions-septic-systems)

If you connect to septic, spread laundry throughout the week, fix leaks, and keep grease and food scraps out of the sinks. Those measures reduce hydraulic and solids loading. [EPA maintenance guidance](https://www.epa.gov/septic/how-care-your-septic-system)

What state/country are you in, how old is the septic system, and do those sinks include the kitchen sink? Those details would help narrow the advice.