What Is a Holding Tank?
A tank that stores toilet waste until it can be handed in at a shore station - the key piece of kit in protected areas where discharge to sea is banned.
A holding tank stores waste from the marine toilet. Göcek/Fethiye is a special environmental protection area: discharging waste to sea is forbidden, and waste is handed in to the station in a logged, Blue Card-tracked system. The tank is the hardware that makes that regime possible.
If ignored, it reminds you of itself in two ways: by overflowing the day the full tank sensor stays silent, or by filling the boat with the smell from a blocked vent.
Tank routine
Empty: on every return to the marina, use the suction hose from the deck fitting to discharge to the station.
Rinse: once a month with fresh water, and once per season with a tank treatment chemical.
Do not rely on the sensor: it is one of the first devices to lie to you when scale and build-up set in, so tank level should also be checked by routine.
If the vent line gets blocked by insects or salt deposits, both odour and vacuum problems start; the small outlet on the hull side should be checked once a year. Never go into winter full - leave it empty with a little antifreeze. Because discharge records are entered on the Blue Card, the answer to 'when did I last empty it?' is recorded as well.