RE: head mistress
With three vent lines, the tank should certainly be getting plenty of air...IF even one of 'em is short, straight and relatively horizontal.
The instructions on the jug of K.O. tell you to add 4 oz/25 gal talk capacity...so 5-6 oz in a 35 gal. tank should be a good
starter amount. Flush it down the toilet, making sure that it gets all the way to the tank. After each pumpout, nominally rinse out the tank and add another 6 oz. I'd recommend putting forward facing clamshells--nice big high ones--over each of your new 1" vents to act as air "scoops."
I hope you didn't buy the gallon of K.O. and then leave it in the car till you were ready to use it...'cuz the bacteria in K.O. can't survive temps over 110...and even in winter, solar heat can easily run the temperature inside a car cabin or trunk up over 150...in the kind of heat we've had (over 100 for more than week and it's predicted to continue through next weekend), you can almost boil water in a car.
It should be ok anywhere on your boat that isn't exposed to direct sunlight.