Try Oderlos
I had a similar problem. Switching to Oderlos solved the problem.Let me preface what I am about to say by saying I respect Peggy, her products and her contributions to HOW. However, due to the small and inadequate venting on my 340, there is not enough oxegen entering the waste tank to get KO working well in my boat. Oderlos (check out the label) produces more oxegen to energize the good stuff so it multiplies and attacks the bad stuff. That's my short and unprofessional recall of the Oderlos product and how it works. And, it DOES work. We can go several weeks without a pumpout now and have no oder problems. It's good stuff. A little more expensive, but worth it. BTW, do not mix the two. Pump your KO tank, flush thoughly, then begin using the Oderlos.Good luck and let me know how it works,Wynn FerrelS/V TranquilityH340