Pilgrim,
Thanks for expounding on the "washing" that Christ does for us.It certainly puts works salvation to death.There is no room left for one to take any credit for aiding Him in the salvation process.
I cite three sources as to the mention of a Gentile slave.
1-R.C. Sproul in his book on John,page 240;....when a rabbi had disciples they typically acted as his servants.However they were never required to wash the rabbi's feet; that task was reserved for slaves.But even some slaves were spared this task.Within Israel,if a Jewish person had a Jewish slave,the slave owner was not permitted to require that slave to wash his feet.Only a Gentile slave could be required to perform such a task.
2-Bible Gateway .com John Commentaries; Having taken off His outer garment,Jesus was left with His tunic,a shorter garment like a long undershirt.Slaves would be so dressed to serve a meal(cf.Lk. 12:37,17:8).Jesus tied a linen cloth around His waist to dry their feet.A Jewish text says this is something a Gentile slave could be required to do,but not a Jewish slave.(Mekilta on Ex.21:2 citing Lev.25:39,46.)
3- Matthew Henry;...... The action itself was mean and servile and that which servants of the lowest rank were required to do.(Gentiles)

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