Raymarine/Raytheon electronics, Sat TV, Yacht Controller
Engines
2003 Caterpillar C-12s Twin Disc Transmissions
If the toilet is leaking water, than more than likely one of the seals in the toilet is leaking. The pump is trying to draw a vacuum and can not. Run your finger around the seal in the toilrt drain and see if there break or if any thing is preventing a good seal. Further down stream I will one of the other members comment on
Mr. Salt
2001 540 CPMY
Caterpillar C-12s
Cape MAy, NJ
320 Sundancer, Zodiac 290 Wave Inflatable Tohatsu 6HP, Boston Whaler 130 Sport
Engines
350 Mag V-Drive - Kohler 5ecd
If the head will not hold water - the leak is in the toilet itself. Otherwise another place to look is the duck bill valves are old or something is sticking in them preventing them from closing completely. Have fun tearing that apart. You may want to run some water through to rinse them before you tear them down.
I had the same problem last summer. The bowl held water, the duckbills were brand new (YUCKY JOB) the pump produced enough pressure after 45 seconds to create solid vacuum. It was the pressure switch on mine. Without any boat info, it's hard to tell you where to look and what to look for.