Winterizing Marine Sanitation Systems

By Brian Gordon, Last updated: 10/14/2020

3 boats covered in snow

Why winterize?

In the event of a hard freeze, residual water in your boat’s sanitation system could turn into ice and cause expensive damage to system components. Protecting marine sanitation systems against freeze damage is actually quite easy. This article will describe how to get the job done.

Step One:

To winterize your sanitation system, start by making sure the holding tank is pumped out. To start “with a clean slate” in the spring, now is the time to give it a through flushing with fresh water.

Step Two:

Remove the raw water intake hose from the seacock and place it in a small bucket with antifreeze.

Step Three:

Flush the head to circulate the antifreeze through the lines and to the holding tank. Then, double clamp the hose back on to the seacock.

Step Four:

Make sure the raw water strainer is purged and filled with antifreeze as well.

NOTE: If you have a waste treatment device such as Raritan’s Electro Scan, it too must be winterized. Improper winter lay up of these devices is a major cause of failure due to freezing of residual water. Follow the manufacturer’s instructions. For complete instructions on Electro Scan winterization, refer to the Electroscan manual.

About Antifreeze

West Marine non-toxic propylene glycol antifreeze is recommended for winterizing potable water, sanitation, air conditioning systems and engines.

There are two types of antifreeze. The first is common automotive antifreeze, such as Prestone, which is ethylene glycol. This type of antifreeze is highly toxic and should not be used for winterizing applications on boats. In place of ethylene glycol, use non-toxic propylene glycol, like West Marine Brand Engine and Water System Antifreeze. For northern regions where the temperature can drop below zero, we recommend antifreeze with a freeze rating of at least -100°F. Why use -100°F antifreeze when the temperature never goes below -50°F? The answer is that what goes into the system as -100°F antifreeze does not come out as -100°F antifreeze. There is always some residual water that lowers the concentration of antifreeze, so the resulting freeze point may be much higher than the rated temperature. The small cost difference between the -50°F, -60°F and -100°F antifreeze is a bargain for the peace of mind you get knowing that your systems will be safe, no matter what the weather. To learn more about antifreeze formulations, check out Antifreeze_ 101.pdf File.

Best Practice for Antifreeze Disposal

Even though Pure Oceans propylene glycol antifreeze is non-toxic, best practice dictates that you not discharge it on to land, into storm drains or directly into the water. After use, dispose of used antifreeze in a manner consistent with federal, state and local regulations.