Over the years we've had a number of cheap porta-potties. They broke, wouldn't flush, leaked, or were hard to dump. After seeing a number of recommendations, seven years ago we purchased a Sanitation Equipment Visa Potty
and it works perfectly. When we sold
and got a built-in bathroom in our Escape
we gave that potty to my sister-in-law and it still works perfect today.
We purchased a second one for the condo I spent three years building. It was used at least 200 days every year by construction workers, friends and myself. I had to go down three flights of stairs to empty (was asked not to take it on the elevator) and never a issue. I sold
it used for $90 after the plumbing had final approval.
Once every spring you just take the plunger out (don't worry it's in the sterile half) and grease it. That's all the maintenance it's needed.
It is spendy, but after our previous experience with porta-potties was worth every penny.