Why does our porta potty smell fine Monday but terrible by Friday?

The smell is the heat overpowering the deodorizer and cooking the waste. Phoenix heat accelerates evaporation and bacterial activity in the holding tank, overwhelming the deodorizer by Friday. Weekly service is standard, but your conditions, 50 people, three standard units and one ADA-compliant unit on blacktop in 100+ degrees, need twice-weekly service. The driver pumps and adds deodorizer, but high use and heat burn through it fast. Ask for mid-week service. A different deodorizer might help slightly, but frequency is the fix. Heat drives the cost: more trips, more fuel, more labor. Shade won’t change much; the tank interior still bakes.

The ammonia smell is the waste breaking down too fast in the heat, and your deodorizer dose is too small for a week of heavy use in Phoenix. The driver adds a standard amount of deodorizer at the Monday service visit, but 50 people fill the holding tank quickly and the heat speeds up bacterial action. Ask for a stronger formaldehyde-free deodorizer formula and a mid-week service. Ray is right about the frequency, but the driver can also adjust the chemical amount per unit if the rental company allows it. Blacktop reflects heat upward, baking the tank from below too. Your setup meets OSHA for 50 workers, but high temps and full tanks need extra attention.