There should be two small round access covers in the bottom of the cockpit locker. (BTW, the 'lazarette' is the area accessible via the two raising lids at the port and stbd stern, down where the rudder post is.) The inner access is for the fuel on/off valve. The outer one is for the fuel gauge sender, and it is this one that you can use to access the interior of the tank.

The tank can be accessed via the aft cabin by removing the wall; however, you'll net get to much that way. You can remove the entire tank that way, though.

Rick, check this out:

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If you do want to remove the tank thru the port side aft cabin, I've found you need to take the fuel sensor out first though or the tank wont slide out, and it helps to have small hands to remove the screws that hold the flanges on the bottom of the tank down on the deck.

As an FYI, if you do this, even if you think you have all the old fuel out and pull the tank, be prepared for some spillage because some always remains and the tanks is very clumsy to handle lieing on your side in the close space... have the wood panels in the bunk out (take my word for it, if fuel gets on them its almost impossible to get the smell out... I had to replace one of mine) and have those oil absorbent pads ready.

For emptying, I take out the fuel sensor and use my electric oil removing pump. Maybe if its empty you can use a flashlight to see into the tank but I suspect it will all look dark. Maybe if you removed the wood panel in the aft cabin, then shined a light in, you'd be able to see more (assuming you have a plastic tank).