Emptying the Fuel Tank

As a result of changing my fuel filters I have determined that it is time to completely empty my diesel fuel tank (18 gallons) on my RT 21'. I bought the boat new 4 years ago and have 189 hours on the engine. Traces of algae on the filters. Need to pump out the fuel as well as whatever algae sediment there is on the bottom of the tank. (I have used additive to address algae consistently over the years.)

I've never done this before. I would greatly appreciate any info from Tugnuts members as to the best equipment to use and an efficient way to handle this task.

Specifically, any suggestions as to the best way to suck up the algae sediment on the bottom of the tank since the only access to the tank that I know of is at the top of the tank.

Thanks in advance,
Tom Borcher
Huntsville, AL

You can make a fuel polishing kit. Basically takes a fuel approved pump and a racor fuel filter setup. You pump the fuel up through the filter and back into the tank. Just keep going around and around until it’s all cleaned up.

There are also services that will come do this for you.

Thanks for the suggestion. I will definitely check this out!
Tom

To polish the fuel you need a big enough pump to get a decent bit of velocity. Racor makes a polishing filter/kit. It is a filter housing with a 12V gear pump mounted on top of it. I bought one to clean up the tank in our boat when we bought it used back in 2014. As I recall it cost me about $500. I bought a series of filter elements, 30, 10, 3 micron. Dosed the tank well with fuel additive and shock level of Biobor. Just hooked it up on the fuel supply and return and ran it. And ran it. And ran it. Tried to agitate it as well as I could while on the trailer. Driving it down a bumpy road and starting/stopping a few times while the pump is running moves the fuel around pretty well.

In retrospect I wouldn't bother with the multiple different filter sizes. I think the filter comes with a 10 micron element. I'd buy one more 10 micron and go for it.

Google Racor P510MAM.

After reading the comments and doing a little more online research, I have to ask:
Isn't it easier and, in the long run, cheaper to simply pump out the 18 gallons into four separate 5-gal diesel fuel containers and then refill the tank with fresh diesel? (Taking the old fuel to a hazardous waste depository.) Considering the price of the polishing pumps and that this is a process one should only have to do once every 4 years or so I'm not sure I see the advantage to polishing????

We had to have the fuel tank on our last boat cleaned and the fuel polished. The service we used had a big filter setup with several filters. They first removed the all of the diesel from the tank into a clean barrel and then they fine filtered the fuel back and forth between two barrels. They also taped clean white lint free clothes onto 1/2” dowel and then they swabbed the tank through the sender access hole. In our case there was approx 120 gallons of fuel so it was worthwhile polishing it. If you have ok access to the top of the tank maybe remove the sender and look inside with a flashlight once it is empty and see if you can see any algae on the sides or bottom of the tank.

A very easy way to clean the tank is to use a oil extraction pump. Remove the fuel pick up tube out of the tank. 3/4 " open end wrench will remove it. Once the tube is removed make up a 1/4" ID tube slightly longer then the depth of the tank. install a tubing compression fitting on the tube with a NPT 3/8" on the opposite end, thread a 3/8 barb/3/8 NPT fitting on the tube fitting, place a 3/8 hose to the barb fitting, attach other end of the hose to the oil pump. Using clean open top 5 gallon pail pump the fuel into the pail 3/4 full. Let the fuel settle for 10 minutes. The water and debris will settle on the bottom of the pail. Using a paint filter pour the fuel slowly into a 5 gallon portable yellow fuel can. Stop when half gallon is left in the pail. Pour remaining in a waste oil container. Repeat procedure until fuel tank is dry. Once tank is dry, pour 2 gallons of the cleaned diesel fuel back in the tank. If the boat is in the water rock the boat to slush the fuel in the tank. On the trailer you may need to use a floor jack. Remove the 2 gallons from the tank let is settle for about 10 minutes, inspect the bottom of the pail for debris. If it looks clean you're done. Check that the fuel pick up.Does not have a screen on the end of it ? If it does remove it . It is not needed for a diesel tank . Install the fuel pick up back in the tank. Pour the filtered fuel back in the tank and fill the tank the rest of the way with fresh fuel and conditioner. Remove and replace the fuel filter primary and secondary. Take the boat out and put some hours on it run through a tank of fuel. Remove and inspect the primary filter for debris. It should be clean. Keep fresh fuel and conditioner in the fuel tank.

Thanks also to NorthernFocus, Shano and BB Marine for the responses. What a great community we have here!