Should be plenty of vent capacity. The pump doesn't move the fluid fast enough to cause a problem unless your vent is clogged. A fast pump is around 30 gpm, which is only about 4 cubic feet per minute, which is nothing for a 5/8" diameter vent line. But if it concerns you, open the trap door. Some hose water in there is a good idea anyway, to clean it out more thoroughly.
I use Happy Camper enzyme in mine, and in the RV's holding tank, and in my keelboat's holding tank when I still had it. Good stuff. Expensive to buy at $22 for the small one, but it's good for 18 treatments of 40 gallons each, which works out to about 8 cents for a 2-1/2 gallon porta-potti tank. The small container my FIL gave me years ago is still going strong; I've never had to buy any.
Happy Camper is popular with the RV crowd, at least those that use any treatment at all. Many don't. But RV holding tanks, as well as marine holding tanks, aren't quite the same thing as a porta-potti, which is more like a mini plastic outhouse.
https://www.happycampers.store/black-tank/