You will be pleased to know that HDB allows individuals and companies who would like to provide car cleaning services at HDB's car parks subject to terms and conditions.
You may refer to HDB's guidelines here: https://www.hdb.gov.sg/cs/infoweb/car-parks/car-parks-for-business-activities/guidelines
You can make an application here: https://www.hdb.gov.sg/cs/infoweb/car-parks/car-parks-for-business-activities/application-procedure
Hope this answers your question.
Propnex Realty Pte Ltd