Adding a personal use bathroom to a detached shop or garage

A personal use shop generally does not require the drainfield to be enlarged, as the net flow to the system will not increase (you are either using the bathroom in the home or in the shop). 

There are four main options for connecting your shop bathroom to an existing septic tank currently serving the home: 

1. Simply connect to the existing septic tank that serves the home. If the shop is located where there is sufficient fall to the existing septic tank (as determined by the Plumbing Code), you may be able to simply connect a pipe from the shop to the existing septic tank, without the need for installing a pump or additional tanks. This will require a Plumbing permit.
2. Install a septic tank at the shop, and connect directly to the existing drainfield serving the house. This requires a minimum amount of fall between the outlet of the tank at the shop and the existing drainfield. See OAR 340-071-0220(11) for required amount of fall. This will require a Plumbing permit to connect the shop to the septic tank, and a Septic permit to install a new tank and new effluent sewer pipe to the drainfield.
3. Install a dosing septic tank and pump near the shop. This is one option if there isn’t sufficient fall between the shop and the existing septic tank or drainfield. This option requires a new tank with a pump to be installed at the shop, so that only effluent (liquid) is pumped to the existing septic tank that serves the house. This is the most common option we see when someone wants to add a bathroom to their shop, and is unable to gravity feed sewage directly to the existing septic tank. This will require a Plumbing permit to connect the shop to the septic tank, and a Septic permit for installation of the new tank and effluent pump.
4. Install a sewage ejector pump in the shop. This is another option if there isn’t sufficient fall between the shop and the existing septic tank. This type of pump turns the sewage into a slurry for transport to a receiving tank. Per DEQ rules (OAR 340-071-0220(3)(d)), a multi-compartment tank is required if you plan to use a sewage ejector pump. As most homes have been installed with a single compartment septic tank, this option will most likely require the existing septic tank be replaced with a multi-compartment tank, or the installation of an additional tank in series with the existing tank. The pump and any connection to a septic tank will require a Plumbing permit, and the installation/addition/replacement of a septic tank requires a Septic permit.