And that could definitely be due to the difference in the tanks' locations on your different boats...the location on your previous boat allowed the vent to supply a lot more oxygen to the tank. Or, if the tank on your previous boat was owner installed, a larger diameter vent line.

If you want to discuss what's needed in more detail than is practical in a forum, send me an email. Meanwhile, you might try using a tank product called Odorlos http://www.odorlos.com/products_info/products_index3.htm (RV supply stores have it for a lot less than marine store prices). The actice ingredient is nitrates, which help to promote oxygen release from organic material--iow, the waste itself--helping to create the aerobic environment needed to prevent odor in the tank.

Thanks for the book plug, Larry. :)