Your metal tank isn't sound...
Urine is eating its way through it. Average life expectancy is about 10 years. If it's younger than that, you can expect it to start to leak at a weld within 2-5 years. If it's original on a '92 boat, I'd replace it BEFORE it starts to leak. (See the thread "holding tank replacement-Legend 37..." in the big boat forum for the worst-case scenario). If you've made the mistake of replacing the original tank with aluminum recently--within the last year or two--you prob'ly have a couple of good years left in it...in which case, go ahead and install the internal sensor. You can't damage the tank by putting a hole in the top of it...just make sure to drill the right size and seal it according to direction. As for your toilet, a 10 year old Jabsco that's never been rebuilt and has prob'ly never seen any lubrication other than pouring vegetable oil down it when it started squeaking is already past rebuilding. Not only are the seals worn out, but the pump cylinder wall has become so worn than new seals won't help much, if at all. The smartest thing to do is replace it.
