How Much Harvested Yeast To Use

So.... I recently upgraded to a 15 gallon system using plastic conical fermenters and pvc yeast catchers. I made a batch of RyePA using 5 packs of Nottingham and harvest about 3 qts of really nice, creamy yeast. I want to brew the same beer with it but am lost on how to go about it. Just dump in the 3 qts? (seems excessive) or seperate it into lesser amounts, like into thirds, make a starter from one third and wash the other two thirds to make them go dormant. I feel like i should know this by now..... any help would be great, thanks.

Mrmalty.com has a yeast calculator for repitching slurry.

I know but it says i only need about a cup, which doesn't seem right. and thats with the meter set at about the halfway point on the 'thickness' scale. i was adding a cushion. the yeast is actually really damn thick, which would change the suggested pitching volume to .8 cups. I dunno, really just doesn't seem right...

I've found this discussion on yeast slurry pitching rates to be very informative:

https://www.homebrewtalk.com/f163/why-not-pitch-your-yeast-cake-166221/