I am wiring up a secondary basement bathroom that calls for a saniflo saniplus toilet, motor has a 7 amp rating (to also be used for the shower). The home run is #12 to an outlet in the bathroom which branches to an outlet in the sitting room which has a freezer (5.6 amp) and a switch from the light, they are both #14. I would like to install another outlet for the saniplus motor and may have to make the home run a junction box and run everything from there. My question is in two parts 1) Should I use #12 wire for the motor to the junction box and 2) should I upgrade the 15 amp breaker to a 20.

You may use #12, but since the existing circuit has some #14 wire, the breaker must remain 15 amp to protect the entire circuit.

Thanks. I had forgot that 14 has to stay at 15 amps. The total amps (freezer,pump)is just over 12 so hopefully all is good.

Glad you brought it up, as I think there will be a problem running all of the load on one 15 amp circuit. You would be better off running a new 20 amp circuit for the pump at least.