Brewhemoth capacity...20 gallon?

Has anyone fermented 20 gallons in one of these fermentors? I contacted them and they said its pushing the limits but did not say it was not doable. They said 20 gallons will take it to the top of the cylinder (20.6 gallons) leaving the dome (estimated volume 1.5 gallons) to hold the krausen.
They also said a blowoff tube would be necessary. I just don't want to buy these if I can't do 20 gallons.

 

Try in here

 

The link is not taking me anywhere. Is it just me?

 

http://www.homebrewtalk.com/f11/brewhemoth-conicals-211245/

Let's see if the above works