The kind I use is liquid, here is a pic.~
The liquid apparently absorbs right away, as opposed to the suppositories. I havent actually used the suppositories myself, so I can't give an actual comparison based on my own experience. But I can certainly tell you the kind of Valium pictured above has been very helpful and that Henry responds well to it. He is dopey for awhile of course, but the Valium certainly ends clusters for Henry. Different dogs respond differently. If your dog is not doing well with the suppository form of Valium, I highly reccomend you ask your vet for the liquid kind. It still goes in the bum, just like the suppository.
While liquid absorbs fast, it does still take 8-10 minutes to kick in.
While on the topic of Valium, I want to show you my emergency seizure kit that I keep in my purse. This is a rigid zip close type deal, that came with my hearing aid. I took all the hearing aid accesories out of it, and put in Henry's seizure stuff instead. In it I have, 3 full doses Phenobarbital in small ziploc bag. (Just in case we get stranded away from home for whatever reason) peanut butter in small ziploc bag, and a fork for administering the Pheno. (Spoon would probably be more ideal) And then the Valium.
p.s. I would love to have comments from people relating what their pet's Valium experience was and which kind was used and etc.