**Connecting the washing machine and sinks to your septic system can be a sound option if the tank and leach field have capacity for the added flow.** Conventional septic systems commonly handle all household wastewater. Your concern is valid because yours has been operating with some of that water diverted elsewhere. [EPA’s explanation of septic systems](https://www.epa.gov/septic/how-septic-systems-work)

The main long-term concern is **overloading the leach field**. Added water can shorten settling time in the tank and saturate the field, potentially causing backups or sewage surfacing. Laundry creates concentrated bursts of flow; EPA recommends spreading loads throughout the week. [EPA maintenance guidance](https://www.epa.gov/septic/how-care-your-septic-system)

Here’s how I would assess the options:

- **Connect to septic:** Have a qualified septic professional review the original design, inspect the system, and assess whether it can handle your combined wastewater flow. Tank size alone doesn’t establish leach-field capacity. The proposed connection should send wastewater through the septic tank before it reaches the field.
- **Install a new drywell:** First confirm why the existing one stopped draining. Have the inlet checked for blockage and the disposal area assessed for soil clogging or groundwater problems. A replacement needs an approved location and suitable soil; another hole nearby may encounter the same conditions.
- **Overflow over the hill:** If this means an open pipe discharging onto the ground, I would avoid committing to it until the local health department confirms the proposal is permissible. Graywater disposal has restrictions, and kitchen-sink water can receive different treatment under local rules. For example, Arizona excludes kitchen-sink water from graywater and prohibits graywater runoff off the property. [Arizona graywater guidance](https://azdeq.gov/graywater)

**My next step would be a septic capacity assessment and a call to the local health department before choosing a bid.** Ask the evaluator to document whether the field can accept the additional flow and whether any upgrades are needed. A cheap connection could become expensive if it overloads an aging field.

What state/country are you in, and do those sinks include the kitchen sink? Those details would help narrow the permitted options.