Number one on every boater’s “green list” should be the proper disposal of human sewage. This single measure can make a noticeable difference in the coastal environment because untreated waste can have a three-fold impact: it can be visually distasteful, it presents a health hazard, and it creates nitrogen pollution which lowers oxygen levels necessary for aquatic life (eutrophication) and causes algal blooms.
Pumping untreated “black water” overboard is also illegal. The Federal Clean Vessel Act Grant Program prohibits boaters from discharging raw, untreated sewage – which is what spews out of most sailboat holding tanks -- within all navigable US waters. That means anywhere within three miles of either US ocean. In very fragile and sensitive regions, specific “No Discharge Zones” have been designated where it is now illegal to dump even treated sewage (see discussion of NDZs).
Just the concept of a holding tank is unpleasant - there‘s no way around it. So keeping the tanks clean and working right is a priority because, as many of us have discovered, no one wants the job of fixing them – for any amount of money! At every pump-out, purge the tank by pumping the head handle(s) about 50-60 times each sending many more gallons of fresh sea water into the tank. And then pump out again – until the outflow is absolutely clear.
An additional step, cribbed from R-V users, suggests mixing water softener and a non-toxic biodegradable detergent into a jug of water, then pumping it into the cleaned out tank. The motion of the boat will slosh this mixture throughout the tank keeping the interior slick so the gunk won’t stick- and it will continue to act on the new black water until the next pump-out. (Note: Don’t combine this recipe with one of the tank treatments described below unless you understand the chemistry of each.) Also, consider a tank monitor – to prevent overfilling.
