Have been using Noflex Digester for a few years now and must admit it works very well for not only controlling holding tank odours but also cleaning the tank and lines. Only drawback is it is rather spendy and difficult to find however ordering on the web has simplified things except for those delivery costs which add even more to the product. https://marinesan.com/noflex-digestor/

Been comparing and reading quite a bit since haul out last fall. Just do some searching for sodium percarbonate and noflex. The active ingredient is Noflex is 80% sodium percarbonate which is an oxidizing agent. Have come across multiple post claiming percarbonate works the same as Noflex however before I say it does I will need a trial season on the water. Probably will work better as I wont be so skimpy on using it any more. Here are a few links discussing the subject. Read between the lines, use your own judgement.

https://www.trawlerforum.com/forums/s31 ... 51219.html

https://www.trawlerforum.com/forums/s31 ... 46357.html

Ordered a 5 gallon pail (40lbs) of the stuff on ebay for $100 delivered to a US address. Advertised as 99% pure. This is a huge savings, about 10x less as those Noflex bottles are only 1lb of product at about $30 each. May even try diluting it with baking soda to the tune of 20%. Got enough product for the rest of my life I believe. https://www.ebay.com/itm/174910196252