Fish Box Drains and Macerator Pumps: Clogs, Check Valves and Odor Control

Drain the box, then rinse it with fresh water and a mild soap and scrub off blood, slime and scales with a soft brush. Pay attention to the drain opening, lid gasket and corners. Leave the lid propped open to dry so mildew and smells do not build up. A fresh-water rinse after every trip prevents most of the problems in this guide.

Scales, small bones and bits of bait clump together and harden as they dry. Cover the drain with a strainer or screen if the box does not have one, scoop out debris before you rinse, and do not clean fish inside the box. Owners often find dried scales packed in the pump or the line when a box will not drain.

With the boat out of the water or the drain above the waterline, run a long zip tie or small plastic drain snake through the drain from the box side, then back-flush from the outside fitting with a garden hose. If the hose connects to a pump, take the hose off the pump first if you can so you do not push debris into the impeller. Skip household drain cleaners; they end up in the water and can attack hoses and fittings.

A check valve or flapper lets water out but stops sea water from flowing back into the box. If the box fills with seawater while you run, or you see water rising in it at rest, the valve may be stuck open with debris, worn or missing. Clean it, make sure it moves freely and seals, and replace it if it is cracked. If it sticks shut, the box will not drain at all.

Turn on the pump switch briefly (with a little water in the box) and listen. Silence usually means a blown fuse, a tripped breaker, a failed switch or a corroded connection. Owners often find a fuse so corroded it falls apart in the holder. With a multimeter, check for battery voltage at the pump wires with the switch on. Voltage there but no sound points to a jammed or dead pump.

When you replace a blown fuse, use the size printed on the pump label, never bigger. A BoatUS surveyor explains that if debris jams the impeller and the fuse is oversized, the stalled motor keeps drawing power, overheats and can start a fire before the fuse ever blows.

Switch off the power. Fish box macerators jam when scales, bones or line wrap around the impeller, or when the pump sat with dried gunk inside. Xylem's Jabsco video for one of its macerators shows a quick check: with power off, pop the rubber cap off the end of the motor and turn the shaft a couple of turns with a flat screwdriver to free the impeller. If the pump then runs, you are back in business; if it runs only a few seconds, the maker sells a service kit; if it will not run at all, the pump may need replacing. Your pump may differ, so check its instructions.

Macerators and impeller pumps are cooled and lubricated by the water they move. Only run the pump with water in the box, and turn it off as soon as the box is empty. Testing a dry pump on the trailer, or leaving it on after the box empties, wears out the impeller and seals.

Look for kinked, collapsed or cracked hoses and loose or rusty clamps, especially on the suction side between the box and the pump; an air leak there makes the pump lose suction. Make sure the hose has no low dips where slime collects. Replace rusty clamps with stainless ones (see hose clamps).

If a box or hatch drain empties into the bilge, fish blood and slime will end up there. Passagemaker describes a boat whose hatch drains emptied into the bilge after a tuna-cleaning session: the bilge filled with a greasy, bloody soup, the smell filled the cabin and the cleanup took many buckets of soapy water. If your boat drains this way, rinse well after every fish, and ask a rigger whether the drains can be re-routed overboard.

Most odor comes from residue in the box, the drain hose, the pump body and around the lid gasket. After a thorough scrub and rinse:

• Flush the drain line with lots of fresh water and a mild soap.
• Passagemaker suggests pouring hydrogen peroxide down a smelly sump drain and letting it sit for a few hours to kill bacteria; the same idea helps a fish box drain line.
• Avoid straight bleach. Passagemaker warns it can react with some plastics, and it can harm pump parts, gaskets and the water you drain into.
• Replace a hose that stays smelly after cleaning; old hoses hold odor.

Pumping fish waste overboard is subject to local laws and marina rules. Sportsman Boats points out that discharge rules vary and many areas want waste taken ashore. Some marinas and harbors do not allow fish cleaning or fish waste discharge at the dock. Check your state and marina rules, and use fish-cleaning stations ashore where they exist.

Lake Champlain Sea Grant's clean boater fact sheet gives a simple rule of thumb: discard fish waste offshore, unless the species has length limits (then keep the fish whole until you are ashore, so it can be measured), and if you clean fish at the marina, use the designated cleaning spot and dispose of the waste the way marina staff direct. Old fishing line that ends up in the fish box goes to a tackle-shop recycling bin, not overboard.

Before storage, rinse and dry every box, prop the lids open, and run the pump briefly with fresh water then stop it when empty. If water can stay trapped in a low pump or hose in freezing weather, drain it or follow your pump maker's winterizing steps. Leave any seacock for the fish box system closed.