Choosing the Right Marine Sanitation Device

Look for these characteristics when buying a boat with an MSD.

When it comes to glitz and glam, commodes are at the bottom of the list behind bilges, barnacles and anchor lockers. But your boat’s head system can make the difference between a boat that’s a beauty and one that stinks. Consider these six factors whether you’re refitting or buying new.

Choices, Choices
Some heads flush with fresh water, some use raw water, and some let you choose via a valve. Using fresh water reduces odors but eats into the limited onboard supply, so being able to choose flush by flush is advantageous.

Get Tanked
The right size tank is hard to quantify. Multiplying the flow rate by an estimate of flushes per day at 10 seconds per flush gets you close. Waste tanks should be constructed of polyethylene, not metal, because urine is corrosive, dooming metal tanks to failure. Look for a waste tank with a wall thickness of at least one-quarter inch, or odor permeation is a distinct possibility.


Type: Manual vs. Electric vs. Vacuum-Flush
Manual heads are simple and easy to fix and cost less. Electric heads have macerators or waste pumps that help prevent clogging, in addition to offering the convenience of button-push flushing. Vacuum-flush marine heads cost more but use much less water than electric models, meaning you can use a smaller waste tank.

Access Points
Easy access to the seacocks is a must for safety. Plus you need to lock them closed, or remove their handles, in no-discharge zones, per federal regulations. Ditto for the Y-valve. Pumps should also grant easy access since periodic cleaning (yech!) and maintenance are required. Also seek out the vented loops; their valves need occasional service too.

Get Hosed
Look for smooth-walled, flexible PVC hose with an inner diameter of at least 1 1/2 inches. Inspect it closely for droops and low spots, where sewage can collect, leading to nasty smells. Vent lines should be as straight (and as short) as possible; plenty of fresh air helps squelch anaerobic bacteria growth, which contributes to offensive odors.


Quick Tip: A head’s discharge through-hull should be installed higher than the intake through-hull.