We use the dry, powdered Aqua Kem-Dri brand of chemicals in our Porta-Potty. You don't need a whole package for each usage but the open (but folded over) packages tend to leak. If the wind is blowing while adding chemicals to the unit, it can create a mess. We now store the powder in a small bottle that we bought at REI which perfectly fits the storage space:
This solution works much better...
'01 Ford EB50p Quigley 4WD
Started out using the liquid (35 years ago :-o ). Switched to powder because of spill concerns. Never happened but sure would make a mess. Now we use the individual pouches. No concern for spilling or wind driven powder. The pouches are little bit pricier then the bulk but sure are convenient for us. Our Pak-A-Potti 6000 (Sears brand) has a 6.1 gal. black water tank so one pouch is a 'fair' trade.