If you are using a porta potti, then I suggest that you get Odorlos treatment for it. It is a calcium nitrate product and it works very well for eliminating odors. Calcium nitrate is what is used in sewage treatment plants to reduce odors. It isn't a perfume or formaldihyde. It is safe for septic and sewage systems. It works by switching the bacteria to producing odorless nitrogen gases instead of the very smelly sulfur based gases. For the small porta potties you only need a small amount, not the full 4 oz that is used in black water tanks.
http://www.amazon.com/Yara-PA352LU52-Od ... B0000AY60Z
Or you can mix your own using Calcium Nitrate fertilizer. http://www.amazon.com/gp/product/B00DVW ... ge_o06_s00
And I also add a little Oxy-Boost Oxygen Bleach as an oxygen source.