Okey,
I second what Bob S did. Why fuel tanks don't come with access ports, I don't know.
OK, so you have to get rid of the fuel, that's a given. New filters, yea. removing your suction tube will give you limited access for any cleaning. I'll take heat for this, but I'm just not crazy about fuel polishing with limited access.
If your fuel is contaminated, your tank bottom is probably crapped up as well. Check the filters you remove, if you see alot of crud particles & grey sludge on the filter, it's also on the bottom.
With an access cut into the top, down the line, you have a visual inspection & easy cleaning ability if necessary. The secret is to first KNOW that you start out with a beautifully clean tank. If unsure on cutting an access, you can have one cut for a reasonable price. Mine is a 6x6" access.
CR