How to cast VARCHAR to BYTEA and vice-versa?

Hello all,

I have a table with a VARCHAR column that I need to convert to a BYTEA.

How do I cast VARCHAR to BYTEA?

The following doesn't seem to work as it yields the 'cannot cast varchar to
bytea' error message:

varchar_data::bytea

On the same topic, how do I do the reverse, that is, how to I cast from
BYTEA back to VARCHAR?

Thanks,
-Michael Moran