Odorlos and K.O. should work immediately
But they won't if you didn't thoroughly rinse ALL of any chemical product out of the tank before you use 'em. I hear from a lot of people who think that it's only necessary to add a little Odorlos to the tank once and that's all till the tank is pumped out. They obviously didn't read the directions...'cuz the directions clearly say that more must be added at least once a week, possibly even more often in very hot weather. It should be added immediately after pumpout...and again when you come back aboard if you pumpout last thing before the boat will sit.Always flush a tank product down the toilet, don't put it down the deck pumpout fitting. 'Cuz if there's any sag or horizontal run in the tank pumpout line, whatever is poured down the the pumpout fitting will make only as far as gravity will take it...then sit there in the line instead of getting into the tank. So add it to the tank via the toilet, making sure pump enough times to move it all the way TO the tank, or it'll just sit the head discharge line too, but only until enough flushes have gone through to get it the rest of way...which isn't great, but better than sitting in the pumpout line till it's pumped out.