It's sole purpose is...
To prevent major pressurized backflows that could overflow a toilet. In the days wen toilets could flush directly overboard, it was intended to prevent disaster if the toilet was flushed against a closed seacock..but only real disaster, not slow seepage. Joker valves were never intended to save boat owners from themselves or--worse yet (maybe)--clueless boat builders who install tanks in locations that are not only way too far from the toilet, but plumbed to run uphill all the way. Way to go, Mick...you've not only asked the right questions, but understand the right solution!
To prevent major pressurized backflows that could overflow a toilet. In the days wen toilets could flush directly overboard, it was intended to prevent disaster if the toilet was flushed against a closed seacock..but only real disaster, not slow seepage. Joker valves were never intended to save boat owners from themselves or--worse yet (maybe)--clueless boat builders who install tanks in locations that are not only way too far from the toilet, but plumbed to run uphill all the way. Way to go, Mick...you've not only asked the right questions, but understand the right solution!
