Why won’t my holding tank pump out?

Dear Boat Doctor,

I am having trouble pumping out my holding tank. The dockside pumps just don’t seem to work very well. I eventually get it pumped, but it takes forever, and I never really know if it’s empty. What’s happening here?                                    

Bill King

Eastpointe, Michigan

Dear Bill,

A marine holding tank is pretty simple, but as you’ve experienced, not foolproof. Looking at the anatomy of the tank, there is an inlet from the head, an outlet to the deck plate and a vent line. The vent allows waste to flow into the closed tank and for waste to be pumped out. The vent keeps the tank from pressuring when filling or drawing a vacuum when emptying.

There are a few steps you can take to get it pumping better. Start by making sure that the pumping system is sealing well to the deck plate. Ideally, you thread a fitting into the deck and clamp on the pump hose. The universal cone fitting that jams into the deck plate hole tends to leak air and not pump well.

Shoreside pumps sometimes struggle to start the flow of waste from the tank. You can trick the system a little by building up some vacuum pressure before you open the valve. Ensure the valve in the pump-out hose is closed and start the dockside pump. Clamp it onto the deck plate fitting and let it run. After a minute or so, quickly open the valve, and the pump will likely give the tank a big slurp, and you’ll be on your way.

Also check the vent; if it’s clogged, any pump will struggle. The potential clog is likely at the tank end; an overfull tank can force waste or paper into the vent. Remove the vent hose from the tank and, root around in it with a straightened coat hanger, and probe into the tank fitting as well.

Should I have my engine oil analyzed?

Dear Boat Doctor,

A friend told me he has been analyzing his diesel engine oil for years to help predict and avoid problems. Is this something you recommend?                                                         

Jenna Baumle

Portsmouth, Virginia

Dear Jenna,

I think oil analysis is cheap insurance. For less than $50 a year, you can have a professional look for any signs of trouble in your oil. The lab will give you a sampling kit into which you put a few ounces of dirty oil and mail it off.  You’ll get a report showing the results within a week or so. As you test over time, they will trend the results for you. It’s a good idea to test once a year during an annual oil change.