How can my two entities do business with each other?

[Jessica Muto]

Good evening,

Sorry if this isn't the right thread for this question, but here goes. We are about to close on our first multifamily property on Monday. It's 11 units, and we are going to long term half and short term the other half. We formed an LLC for this property with separate bank accounts and everything. It's great, but obviously not a lot of money in those accounts right now until income starts coming in, probably in a month or two while we get everything up and running.

Here's the main question: we also own a plumbing company (S corp) and our plumbing company is going to do the plumbing work for the multifamily unit. I get the concept of having one entity sign a contract with the other, and we can do that just like we would do with any customer. Maybe we'll give ourselves a small discount, but otherwise it should be all very clear and separate. BUT the real estate can't afford to pay for the whole plumbing job right out of the gate. If we were paying another vendor for this , we might just use the HELOC, but it doesn't make sense to pay ourselves out of the HELOC and then pay ourselves back with interest.

Is this making sense? Should the plumbing company do the work and bill for it later, or accept payments over time? I'm not at all sure what tax issues I should be thinking about it, if any. 

Hopefully this makes sense, and you all have run into this kind of thing before. Any ideas are welcome! Thanks!