320Driver, there are or should be aircraft wash prep and post wash work cards that WILL be signed by an authorised/approved person. The actual task as such is normally carried out by companies with dedicated a/c wash teams, although they are not likely to be a/c mech/tech or eng. Depending on the type of wash it may neccessitate, landing gear and/or flying control re-lubrication.
Post wash card should include checking all the ports/probes etc.