And thou shalt bring Aaron and his sons to the door of the tabernacle of the testimony, and having washed them with water, Thou shalt put on them the holy vestments, that they may minister to me, and that the unction of them may prosper to an everlasting priesthood.
The washing of the hands and feet is a Jewish thing. Our Blessed Saviour was carrying out a very Jewish action - he was preparing his Apostles for the everlasting priesthood of the new and Eternal Covenant.
The Congregation for Divine Worship and Discipline of the Sacraments issued this 2008 judgment with regards to the ongoing, world-wide abuse of the mandatum.
Further information may be obtained visiting this excellent website: Stop Mandatum Abuse