We have Galley Maid Saltwater heads on Good Karma. This means when we flush, we suck up water from the Ocean/ICW and it flushes the toilet. Good news they work great, bad news they use funky water and a lot of it. SO, the holding tanks fill quickly making pumpouts even with 184 gallon capacity something to consider weekly!
I found a product called ZAAL Noflex Digestor to help solve the problem of Good Karma previously being a dock queen and not getting regular pumpouts. Well, after using Zaal (1 tablespoon in each head after a pumpout) the first time we went 10 days! Second pumpout 2 weeks and it still could have gone a little longer. I feel it's eating up the layer of funk that was in there and we're getting closer to clean tanks. Recently, we had another couple on the boat for 5 days and we're still good after 10 days! It's also environmentally friendly.