Most if not all pressure washing type work would fall under a prime contractor. It probably will not be easy to find as most prime contractors cover a wide variety of services for DOD and DOE. Most primes are large companies that have contracts for heavy civil and structural type of work. They also usually have either in place pre negotiated sub contractors or in house capabilities.
A good place to start would be to get a DUNS # and make sure that your PAYDEX rating is in place. The primes that we work for require a 2A rating or higher, although some will let a BA rating.
I am not sure but I think that if you are MBE classified, then that will count towards the prime contractors MBE - WBE - 8A - SDE - DBE total goal. Although I am not sure if they will be using these certs anymore. But never hurts to inquire.
Be prepared to provide bank statements, letters of credit, and full disclosure. DO NOT LIE you will likely be put on a lifetime black list of sorts.
If you have military back round there may besome programs out there to help you attain contracts.
Also check with you local SCORE chapter, some of those guys have awsome connections and info.
Good luck,
Joe