Can a porta potty sit on a slope if it is shimmed, or does it need to be flat?

A standard portable toilet needs to sit level, not just propped until it looks upright. On a firm 10-degree grade you can usually get there with wood blocks under the downhill skids, but the cabin has to end up plumb so the door latches and the tank fluid sits even.

If the unit stays tilted, the door hangs open or swings shut on its own, liquid pools on the low side of the tank so the fill looks wrong, and the floor feels tippy when someone steps in. A weekly service visit still works as long as the vacuum truck can reach the unit and the cabinet does not rock while the driver pumps.

Most crews will place a standard unit on a slope when the ground is firm and they can level it with blocking before they leave. Tell them about the grade when you book so they bring enough wood and do not refuse the spot on arrival. Ask them to set blocks under the downhill skid until a bubble level on the floor reads flat. Do not leave it on a noticeable lean for the whole summer.

A standard portable toilet needs to sit level. Wood shims under the downhill skids are fine when they get the cabin plumb. They are not fine when they just prop one corner until it looks upright from the driveway.

We had a standard unit dropped on a graded gravel pad that looked flat until someone stood inside. The door would not latch, and the liquid in the holding tank sat on the low side so the fill looked wrong. The driver came back with blocks, set them under the downhill skid, and checked the floor with a bubble level before he left. After that the door worked and the weekly service visit went without drama.

Tell the rental company about the slope when you book so they bring blocking. Firm ground with truck access is usually placeable. Soft mud or a rocking cabinet is not. Do not leave it on a lean for the summer. A tippy floor is how someone takes a fall climbing in with work boots.