Park the RV and open the holding tank panel, which is typically in the rear-right side of the rig. Locate the set of holding tanks -- black, gray and fresh. Check each tank for bulging on the sides and top. If bulging is there, air needs to be let out of the tank.
Open the tank intake-flow tops on the outside of the RV. This is where you put the fresh water hose, or where you connect the drains for the gray or black water tanks. Leave the tops off.
Go back to the panel and put on work gloves. This is especially important when handling the gray and black water tanks because contaminants may be present.
Push and squeeze the plastic tanks as much as possible. The plastic takes time to mold back to original shape once it bulges out, so if possible, leave the RV in a cool or shady area and let the air filter out through the flow-valves and allow the tanks to reshape.
Place the caps back onto the flow valves and close the panel.
