Aluminum Diesel Tank Cleaning

[All is found]

We are have hired someone through our boat broker to clean our fuel tanks as we have bacterial sludge.
Problem is there are not really any inspection ports on the rectangular tank.
(Leopard 2012 Catamaran). The fellow we hired has stated he will cut a hole in top...not sure what else - if he's planning to weld a flange??
I am concerned about:
1) Qualification requirements for this work?
2) Should tank be removed from boat?
3) There are 2 side baffles in tank - is one port going to suffice for the tank cleaning/inspection?
Any advice!?
There is a manufacturer's plate/stamp on the tank...can we mess with it at all?
Thanks in advance for your help.

[Gary Mc]

My aluminum fuel tank has an inspection port. It is just a round hole and has a plate with gasket that covers it. The plate is held there with machine screws that are tapped into the top of the tank.
No reason to have to weld that I can see.

I was lucky in that I could get my tank out of the boat for cleaning. My son spent a fair bit of time on it but got it all nice and shiny.

[Paul Elliott]

We added a second inspection port to our 75-gallon aluminum diesel tank (easy access to the original port was blocked). We didn't even drain the tank when we sawed the circular hole in the top, and used a shop-vac to suck up what cuttings we could. I got a circular aluminum top-plate from the boat manufacturer (not sure where they got it from), but it's just a thick aluminum disc with regularly-spaced holes around the perimeter. I drilled and tapped holes in the tank to march the cover holes and use SS machine screws with a cork gasket to keep the cover plate sealed. There was some aluminum debris that went to the bottom of the tank, but it just sat there until I cleaned it out some time later when I drained the tank for a cleaning.

Don't try this with a gas tank!

The new inspection port doesn't let me directly access the entire tank, due to tank baffles, but I can reach inside and rag-wipe almost all of it. I do somewhat regular testing of the tank condition using a drill-pump and a semi-rigid plastic cube to extract fuel samples from the bottom of the tank. If I find significant water or bacterial sludge I drain the tank using the drill-pump and a lot of jerry cans.

[puffcard]

I had the black diesel algae, where it looked like black fur on the sides of the tank. I get access thru the fuel level sending unit. Used Biobor JF had excellent results. Now tank is very clean. Most algae is caused by water, check the fill cap for the required oring, bet it's missing.

[Vasco]

If you can remove the tank then that's your best bet. Remove them and take them to a rad shop for cleaning. Second best, a good fuel polishing guy might be able to get them clean. One did mine going through the fuel guage sender hole. But my tank did not have baffles. I have used Startron since then and after five years no problems.

[a64pilot]

If it’s a Pro, then they know what they are doing, this is way more common than you think.
After it’s cleaned, use Bio-Bor Jf or it’s equal, and use it at the shock mix ratio for a few tanks to get it all, it’s everywhere, in the lines, everywhere.
Buy a dozen filters just in case and change as necessary, the more fuel you use, the cleaner and better things will be.
However, always use a biocide, even if your sure you will burn the fuel soon, never go without, and you will never have a problem again.

[All is found]

Thanks All!!! Love this forum - lots of great advice! Appreciated!!