I have just completed the same chore but with Aluminium tanks
. Here is my experience and hopefully you will learn from my mistakes
were under cabinets so I was limited as to where I could drill the holes. The best tool for cutting the tanks is an 8" hole saw. Any smaller hole and it is difficult to get your arm into the tank to clean out the gunk. I had had my tanks cleaned professinally with a service
like Paul was talking about and it didn't work so well. I had a welder build a rectangle from 1/2" x 1" aluminum
and then cover that with 1/4" plate. I then drilled the holes about every 1 1/2" around the perimiter. I tried to seal this with permatex. It did not work well. I finally had to buy some nitrate gasket material. Conclusion. Unless you really like making things yourself I would buyt the premade diesel access ports
. Seabuilt - Access Plate Systems
When laying out your main hole make sure that there is enough room away from the edges and the baffles to get the rim of the ports to set properly. If I were to do it again I would use self tapping screws to hold the port lid in place and then drill the screw holes of the lid thru the lid itself to ensure accuracy.
The baffles can be difficult to locate since they do not neccissarily weld the baffle to the topp of the tank. I used an existing hole in the tank and then was able to track down the baffle welds on the side of the tank.
To clean the tanks I used the following tools: 1) plastic scraper ( to get the big chunks out), 2) rags to sop up the last bits of diesel 3) paper towels and multipurpose cleaner to get more stuff out of the tank 4) scotch brite pads to get all the scunge off the sides and bottom of the tanks, 5) a shop vac to suck out all the metal filings out of the tank when there was no diesel left in the tank. It worked well but it was very time consuming.
Here is a link to a couple of other threads:
Fuel Tank Acces Ports
What's in Your Tank
Good luck let us know how it worked out.