To the OP, sorry to here your woes,All I can say is Air head - really. Skip the tank and start composting - no float valve/switch/pump out required.
I am amused that these rants against conventional holding tanks systems always start with...Allow me to vent:
I also had a 15gal holding tank, attached to it of all things was a Jabsco macerating electric toilet (BIG flushes). You may imagine the capacity was virtually nil with that little rig. Add to that, the poorly thought out way the system was plumbed.
I had one overflow (quel gachis!), I was hesitant to use the head because of the small capacity, and I could always smell it.
Exactly a week ago Friday, I removed the entire system, and yes even though the tank was empty there was still some stuff in the hoses, so be aware of that. The removal was one of the vilest jobs I've ever had to endure. The formalin (ergo "tank treatment") in the holding tank....
ASTM journals and sailing mags both. Chemical engineer by training and long experience.pdqaltair,
it's always amazing to me that people like you, who know so very much, only expound your knowledge on Internet fora, rather than being published in peer-reviewed publications, or other publications which pay for such knowledge.