I like buying them at 90-95% face value and combining that with other discounts

I get the whole, it's Christmas thing, and for that reason I'd give them to the end of the year, or 30-days from when you took ownership, but you can't afford to have them stay at a discounted rate.

I do this for my primary dwelling as well so I get a discount for multiple properties.  

I was looking for some lenders that would fund 100% of the purchase and rehab if the purchase was discounted enough that is was a smoking hot deal.

You'll have access to auctions and discounted freight. 

Since then I've been going out and looking around neighborhoods for For rent signs (frustrated landlords) and looking for houses that are dilapidated for me to get a discounted price.

They most likely would be who I contract for labor seeing I'd get a good discount.

YoY discount from list price?

Not sure how much starting capital you have, but I think too many people discount the Seattle area as a place to invest in.  

Your answer is just to shop it to other buyers at your new discount and disclose the septic IMO.