The PO was wrong...
It's NOT legal to dump it overboard unless it's used as it was designed be used...and that means using ONLY TDX, and ONLY as directed. Here's how it's supposed to work:The tank, which has a macerator inside it, holds 9 gallons. Waste goes into it, the same as it would into any other holding tank. It has a tank level indicator that lets you know how much is in it--that light panel is separate from the "treat, hold" etc panel. As you've noticed, there's a holder for a gallon jug of TDX...the wires are connected to a pump that automatically injects a pint of TDX into the tank when the "treat/hold" or treat/discharge" switch is activated, then starts the macerator inside the tank. That macerator runs for 20 minutes...then, if it's wired correctly, in the "treat/discharge" mode the overboard discharge pump kicks on to dump the tank...in the "treat/hold" mode, it just shuts down. As soon as the overboard discharge pump has emptied the tank, the pump automatically puts another pint of TDX into the tank (iow, "treat" uses a quart of it--one pint at the end of each treatment cycle, a second one at the beginning of each one. So unless ALL the following is true--1. the macerator inside the tank is working, 2. the pump that puts TDX in the tank is working, 3. the chemical is TDX, and 4. the system is working exactly as I described above--it is NOT legal to dump the tank inside the "3 mile limit." SeaLand bought Mansfield in 1984, so anything with the Mansfield brand name on it has to be at LEAST 20 years old. No parts have been available for anything bearing the Mansfield brand name for more than 10 years...so there's no way to get it working again the way it's supposed to...so for all practical purposes, all you really have is a 9 gallon holding tank that can only be emptied by pumpout within 3 miles of the whole US coastline, a bunch of useless jury-rigged plumbing, and some equally using wiring that, from your description of it, is most likely a fire waiting to start.So in light of all that, coupled with the fact that TDX costs about $20/gal and only treats 4 tankfuls/gal, IMO the smartest thing you can do is pull it out and replace it with either a plain ol' holding tank that can either be pumped out or dumped at sea, or a Lectra/San, which doesn't use ANY chemicals, but creates chlorine by charging the ions in salt water with electrical current. I'd also replace the toilet and all the sanitation hoses...'cuz I doubt if they're in any better shape than the TDX system.