How do you tell party guests to use the porta potty and not the house bathroom?

You tell guests to use the porta potty by making it the only convenient option and communicating clearly. Lock the door to the house and put a sign on it that says 'Please use the outdoor restroom' with an arrow pointing toward the unit. Place another sign on the porta potty itself that says 'Restroom' so it's obvious. Position the unit near the party area, not hidden away, so guests see it naturally. With food and drinks for six hours, one standard unit is tight for 60 people; the event planning guideline starts at one unit per 50 to 75 people for a four-hour event, and you add units for alcohol and longer duration. A deluxe unit with a sink isn't necessary if you have a separate handwash station, but it does offer a more comfortable experience with flushing and a mirror. The standard unit's holding tank holds 50 to 70 gallons, which should be sufficient for a one-day event without service, but heavy use or hot weather can fill it faster.

Nina is right about locking the door and signs, but also station a host near the house entrance to redirect guests politely. One standard portable toilet is borderline for 60 people with drinks over six hours; the event guideline starts at one unit per 50 to 75 people for four hours, and you add units for alcohol and longer duration. Expect the holding tank to handle it, but heavy use risks capacity. Your separate handwash station covers sanitation, so a deluxe unit isn't necessary.