Some Poskim forbid removing the toilet tank cover on Shabbos, being the tank is Mechuber (attached) to the ground.*
Mori V'rabi Hagaon Harav Shlomo Miller Shlita argues.
He holds that since the cover is designed to be removed easily,it is considered as if it has a handle. A cover with a handle may be removed from a Bor (pit) that is Mechuber L'karka.** (ground)
The tank cover is considered a Keli (vessel) and not בטל to the
Mechuber tank .
Therefore there is no סותר or מוקצה.
** או"ח ש"ח י'