Check your seals and ensure you have a good bowl seal of water when opening the trap quickly. We did 5 days this weekend without chemicals and were fine. We have ALWAYS used chemicals prior but read of many saying they are not necessary provided we had good seals, it held water and we kind of caused a seal with the water as we opened and flushed quick. Worked like a charm and no odour all weekend. Proved to us we can operate without chemicals which at the end of the day only mask over the smell but it's still kind of there underlying when using chemicals or air freshers anyway.