Why does our construction site porta potty smell worse on Monday mornings after the weekend?

The weekend odor buildup comes from the deodorizer going stale in the heat and the unit's ventilation not moving enough air. The holding tank is a sealed environment, but it is not airtight.

A standard portable toilet has a vent stack to let gases escape. On a quiet weekend with no door openings, very little air flows through that vent. The summer sun heats the plastic unit like an oven. The heat cooks the waste, releasing more gas, and it also breaks down the fragrance and surfactants in the deodorizer. By Monday, the deodorizer has lost its punch and the concentrated gases have nowhere to go.

Your Friday service visit leaves the tank clean and the deodorizer fresh, but that formula is designed for a week of regular use, where opening the door frequently draws fresh air in and pushes stale air out. For a unit that sits unused for two full days in hot weather, a mid-week service would eliminate the problem. The rental company could also check that the vent is clear and not blocked by dust or a spider web.