What will physically fit underneath.

The gap under a bath is the tightest anywhere.

So the body is shallow by necessity.

And the outlet turns immediately.

Fit comes before every other consideration.

Because the trap is unreachable without it.

A bath in a tiled recess with a sealed panel.

Can only be reached by breaking something.

Access is part of the specification.

And it is routinely left out of it.

Because they are fitted blind.

By feel, in a confined space.

Often after the bath is in position.

A joint not quite seated drips into a void.

Where nobody sees it for months.

Fill the bath and let it out in one go.

Before any panel is fitted.

A trickle tests almost nothing.

Full bore finds a loose joint at once.

That test is the quality control.

Hair, almost exclusively.

It gathers at the waste and in the trap.

So clearing from above matters here.

More than in any other position.

Choose a waste that opens up.