I would suggest the following -
In our G-26 we replaced the head and holding tank with a large capacity fixed "portapottie". It gives us 62 flushes which is more than the originally factory installed holding tank would allow. Easy to mount into place, never any odours, has air vent tube for vent, has pump out piped to Grampian deck installed fitting.Check the archive here on this site - type in "permanent mounted portapotties" and you will find a large amount of information on this very topic.BTW - I am not aware of any non-discharge zone anywhere within close to a thousand miles of your location so don't even think about it.Cheers,JimQ26 G-26 #583 Sam's Closin'time