How do I grow a large rental portfolio without down payments?

[Akshar Agarwal]

I wish to grow a large rental portfolio for passive cash flow, and the BRRRR strategy is fine but how do I complete the Buy portion if I can't keep saving up 20-50k and putting it into a property? Ideally, refinancing 70% ARV would return the down payment but that alone takes lots of time to complete (6-8 months post-purchase). So how do I grow a rental portfolio quickly?