I've never heard it taught that baptism washes away sin. It is ,however, you symbolically renouncing the flesh and putting to death your old man. It is also a surrender of the temple of your body to the authority of the One who purchased it as his dwelling. It is a step towards the new birth. We simply cannot ignore Jesus' own words...
He who believes and is baptized shall be saved (saved by "
washing of new birth and renewing of the Holy Ghost" as Paul said in
Titus 3:5. If we are not willing to renounce the old man, we cannot expect to receive the new man.)