I have a Ground Effect Spinal Tap & everything fits nicely. You don't have to put the hydration pack in...
http://www.groundeffect.co.nz/produc...il-SPI-BAG.htm
Whoops, sorry...It helps if i read posts properly...:0
I can put my saddle pouch on my mtb but don't normally as i'm bad & don't drink enough with just a water bottle to try & reach.