Ground serving the toilet is one of the most dreaded jobs of maintaining an aircraft. Whether the job falls to you or your favorite Line representative, make that job easier by coating the inside of the service cap with LPS3. This water displacement/corrosion inhibitor product will not only make it easier to remove but will prolong the life of the cap.
And while you’re at it, take a quick look at the CIC, Corrosion Inhibit Compound, in the servicing box structure and reapply if needed.
A little bit of maintenance in this small area goes a long way.