Some Poskim forbid removing the toilet tank cover on Shabbos,
being the tank is מחובר לקרקע (attached to the ground).*
Mori V'rabi Hagaon Harav Shlomo Miller Shlita, argues and
holds, 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 בור (pit) which is מחובר לקרקע.**
The tank cover is considered a כלי (vessel) and not בטל to the
מחובר tank.Therefore there is no סותר or מוקצה.