Answer:
I believe the best option to be the third one: use a plural verb with a collective subject functioning as individual parts.
Explanation:
The subject of the sentence we are studying here is "the dance crew". The word "crew" is singular and, because of that, we would expect the verb to conjugated in the singular form as well - "washes". However, since "crew" is a collective noun - it indicates a collection or a number of things or people -, there are two possible ways to conjugate verbs with it. If we think of crew as a unit, the verb shall be singular. But, if we think of it as the individuals who are part of, each one of them performing an action, then the verb shall be in the plural form.
In conclusion, if the verb is in its plural form - "wash" -, the best explanation for its subject-verb agreement is the third option:
use a plural verb with a collective subject functioning as individual parts
