Marine Toilet Won't Flush or Pump — How to Fix It

My manual marine head won't pump or flush — what's clogged and how do I clear it?

On a manual marine head, "won't pump" is almost always one of three things: a closed seacock (no water in), a blocked discharge line (no water out — usually calcium/struvite scale or paper/non-flushables), or worn pump valves/seals losing their prime. The fastest diagnosis is the pump lever feel: stiff with no travel points downstream to a blocked discharge or scaled hose; loose and spongy with no suction points upstream to a closed intake seacock or bad pump valves. Most clogs are scale buildup where urine and seawater meet, plus things that should never go down a head — wipes, tampons, paper towels. Confirm both seacocks (intake and discharge) are open before you take anything apart.

ℹ️ Reference only: For general reference only. This guide does not guarantee any result — every home is different. Verify against your local building codes and a licensed professional before acting, especially for electrical, gas, plumbing, structural, or roof work.

💵 $15-$40 for descaler/vinegar and clamps; $30-$90 for a manufacturer pump rebuild/joker-valve kit (DIY). $150-$400 at a marine shop for a pump rebuild or service call; hose replacement runs $300-$800+ depending on access and how much sanitation hose is needed. ⏱ 15 minutes to check seacocks and clear a soft clog; 1-2 hours for a pump rebuild; half a day or more to replace scaled discharge hose in tight spaces. ● Use caution

Safety: The head's intake and discharge lines connect to thru-hulls below the waterline. Opening the pump or hose with a seacock open can let water into the boat and sink it — close BOTH seacocks before disassembly and verify they actually shut. Double-clamp every below-waterline hose joint with all-316-stainless clamps (band and screw both stainless, per ABYC) and check for leaks before leaving the boat. Marine sanitation systems carry pathogens and produce hydrogen sulfide and methane in tanks and lines — both toxic, and methane is flammable/explosive: wear gloves and eye protection, ventilate the space, keep open flame and ignition sources away, and don't work a holding tank in a confined area without airflow. Never use bleach or petroleum products in the head — they destroy the joker valve and seals. Never discharge untreated sewage in a no-discharge zone or within the 3-mile limit; keep any overboard Y-valve secured closed in those waters and know your MSD rules.

Common causes

Closed or stuck intake seacock, or a clogged intake strainer/joker valve so the pump can't draw raw water (no water entering the bowl) (most common)
Quick check:
Calcium/struvite scale buildup in the discharge hose and pump where urine meets seawater, narrowing or blocking the line (most common)
Quick check:
Non-flushable items jammed in the pump or discharge — wipes, paper towels, tampons, excess toilet paper (common)
Quick check:
Worn or torn joker (duckbill) valve or pump piston seals/O-rings, so the pump loses prime and won't move water either direction (common)
Quick check:
Full holding tank or closed/clogged tank vent creating backpressure so nothing will pump down (less common)
Quick check:

How to fix it

Check the easy stuff first: confirm the intake seacock AND the discharge seacock (or Y-valve to the holding tank) are both fully open. A closed seacock is the single most common cause and costs nothing to rule out. While you're there, glance at the intake strainer for weed or debris.
Read the lever. Pump on the wet/flush setting: if the handle is stiff and won't travel, the blockage is downstream (discharge hose/pump/joker valve or a full tank/blocked vent). If the handle moves freely but no water enters the bowl, the problem is upstream (closed intake, clogged strainer, lost prime, or worn pump valves). This tells you which end to open up.
Try to clear a soft clog without disassembly: pour a bucket of fresh water into the bowl and pump slowly to push the obstruction through. Never force the handle hard — you'll crack the pump body or blow a hose off a barb and flood the boat.
If you suspect scale, descale it: with the system set to pump to a legal pump-out facility or holding tank (not overboard), draw a white-vinegar or marine-rated descaler-and-water mix through the pump, let it sit, then pump it through, and repeat. Scale is the slow-strangulation cause and the usual reason an old head 'gradually' got harder to pump. Do NOT use bleach or petroleum-based products in the head — they harden, swell, and crack the joker valve and rubber seals; stick to vinegar or a descaler labeled safe for marine sanitation systems.
Rebuild the pump if valves are the issue. Buy the manufacturer's marine service/rebuild kit for your exact model (e.g., Jabsco/Xylem, Raritan, Groco) — it includes the joker valve, flap valve, piston seals and O-rings. Close BOTH seacocks first and verify they actually shut. Disassemble the pump, clear the bore of scale and debris, replace all valves and seals, reassemble. Lubricate seals only with a silicone or Teflon-based (non-petroleum) lubricant — petroleum jelly destroys rubber. The joker valve is the #1 wear part and a cheap, common fix.
If the discharge hose itself is scaled solid (you can tap it and hear/feel hard crust, or it won't flex), it must be replaced. Use marine sanitation hose rated for the job (e.g., Trident/Shields sanitation hose) — not cheap PVC, which goes permeable and stinks. Double-clamp every below-waterline connection with all-316-stainless hose clamps (band AND screw housing stainless) per ABYC. Route hose without sags that trap waste.
Reopen the seacocks, flush several times with the bilge in view, and check every joint for leaks before leaving the boat unattended. Confirm the head flushes clean and pumps dry in both directions.

DIY or call a pro?

Clearing a closed seacock, descaling, and rebuilding the pump with a manufacturer kit are well within reach of a competent owner with basic tools — these are the great majority of cases. Move to a pro if the discharge hose needs replacing in cramped/awkward runs, if a below-waterline thru-hull/seacock is seized or weeping, if there's a holding-tank or vent problem you can't trace, or if you're not confident double-clamping below-waterline connections correctly. Getting a thru-hull connection wrong can sink the boat.

Tools & parts

Manufacturer pump service/rebuild kit for your exact head model (joker valve, flap valve, piston seals, O-rings) — e.g., Jabsco/Xylem, Raritan, Groco
Marine-rated descaler or white vinegar (no bleach)
Replacement marine sanitation hose if needed (e.g., Trident/Shields), correct ID for your head
All-316-stainless hose clamps (two per below-waterline connection; verify the screw housing is stainless too)
Screwdrivers, nut drivers/sockets, and adjustable wrench for the pump assembly
Nitrile gloves and eye protection
Bucket of fresh water, rags, and a silicone or Teflon-based (non-petroleum) lubricant for seals on reassembly

Keep a record of every fix you make — what broke, what it cost, how you solved it.

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Based on: BoatUS / BoatUS Foundation; ABYC (American Boat & Yacht Council) — H-27 seacocks/thru-hulls, H-2 ventilation/sanitation; USCG / USCG Auxiliary (marine sanitation device and no-discharge-zone regulations, 33 CFR 159); Head and pump manufacturer service guidance (Jabsco/Xylem, Raritan, Groco)

General marine-maintenance guidance, not a substitute for a qualified marine technician or surveyor. Boats and conditions vary; for fuel, electrical, fire, or structural issues — or anything safety-critical — consult a professional. Always follow your engine and equipment manuals.