How do people aquire multiple units in such a short period?

[Jeremy England]

I am a former builder, did one flip REO property about 10 years ago, that was financed with my business line of credit. I've been doing research on house flipping and buy hold investing (mostly flipping). But anyway, one thing I don't seem to understand about buy/hold. How is it that so many people are able to purchase multiple properties in such short periods? I understand getting value when you buy and all that. However, at some point, properties and repairs need to be paid for. So as I understand it the deal works like this:

Find a property (I know, easier said than done but humor me)

Get a great price well below market

Arrange financing or pay cash. This is the part where I get confused. If I pay cash for the place, well, that's pretty much ALL my cash. How will I get more properties? OK say I get financed via a HML or private money. Get the property, do the repairs put a tenant in. How is the lender being paid back? Refinancing and pulling equity out? Say I get a property for 70k and it takes 30k repairs and now the value is 140k. Am I getting a mtg for 100k to pay the lender back and a payment of say 600 a month. Collect rent for 850/mo, cashflowing 250 ( I know there are other expenses but stay with me).

So now I want another property and go do the same thing again.  But when I go to refinance, will the bank just keep refinancing the properties that I control?  Then there is the debt you incur.  Is the answer just to keep racking up mtg after mtg as long as the cashflow is good? 

Tell me what I'm missing here. 

Thanks

[Jason G.]

@Jeremy England, we saved for the down payment on our first SFH investment property and for a portion of our second. Took out a HELOC on our primary and used it to cover the remainder of the down payment on the second SFH. The third SFH down payment came completely from the HELOC. Our fourth (which we have yet to find) will also be paid using the HELOC and we have around 40k in reserves. Rent covers property manager, mortgage, HELOC interest payments, vacancy, maintenance, and CapEx. Remainder goes into saving for next property plus we are able to put aside almost 3k a month for future investments from our W2 incomes and also our bonuses and tax refunds. So that is how we are funding our investments, all with 20% conventional mortgages. Everything is buy and hold.