Which of the following fixtures' final waste connection cannot be connected by the use of a compression gasket?

The final waste connection for a bathtub cannot be made using a compression gasket due to the plumbing code requirements that focus on the potential for leaks and the need for secure, watertight connections. Bathtubs typically require a more robust sealing method to ensure that water does not escape, as they deal with larger volumes of water and the potential for standing water.

The other fixtures mentioned, such as roof drains, floor drains, and sinks, can often utilize compression gaskets for their connections due to the nature of their drainage applications and lower water retention. In particular, these fixtures might be situated in locations that allow for the effective use of gaskets without the same risk of leaks that might arise with a bathtub installation. Therefore, the bathtub's requirement for a secure mechanical joint or a solvent-welded connection highlights the importance of adhering to specific plumbing code standards for more significant plumbing fixtures to mitigate issues related to leaks and water damage.