I have been using a Source WPLS low profile 3L bladder in my Revelate bag. The internal rib stops it bulging,the covered tube stops gunk growing in the pipe and the QR fittings are really good....I am looking at a longer hose just for frame bag use (it normally gets used in my Goruck GR1 pack....I bought it from Goruck with the pack as they recommend it)
Add in the easy clean "open the entire top and get your hand in" top opening and it is a no-brainer!
http://source-military.com/product.php?id_product=82SSP