It has been 15 years since I last changed the gasket under a sending unit but if I remember correctly it is just a twist lock. I seem to remember using a drift pin to knock a tab to make the unit turn slightly. (on the other hand it could have been some other car!)
Hopefully somebody else can chime in.
However, if you do get it out definitely change the gasket under the sending unit and clean well with a carb cleaner to get the varnish off if there is any.
Steve