Washing yeast with Wort

[Clearwall]

Has anyone done this instead of using water? I have an idea but I need to use something from two different batches. I want to use the yeast cake from an American Ale and the 2nd runnings from a Dunkel to make a high gravity Marzen.

Curious about how much wort I would need to do this effectively? I need as much beer as possible out of all three batches. Would 1/2 gallon be enough, do you think?

 

[Bellybuster]

if you use wort it will start fermenting causing the washing to be moot.
Just use some of the yeast cake as is.

Just for interest it has been shown that washing has little benefit.