Intro problem... NEED HELP!

[Ratskateer]

So, I got a new rat a while ago, and I've been gradually introing him to my old rat for a little while now.  By this time, I have their cages next to each other, and every once in a while, I'll let them into one another's cages for a couple of hours. 
So, I've decided to start putting them together now; it's been a few weeks, I figured it would be easy.  So, for the past few days I've been putting them together in my bathtub for 20-30 minutes.  However, I'm don't think it's going too well; not that I know too well, seeing as I've never done any intros before, but I've read about them.. and it doesn't seem quite right.
My old guy, Rolo, will start to groom the new one, Peppermint, a little; then Peppermint will freak out and they will start squeaking like crazy and jumping around the tub; I once saw Peppermint jump about half a foot in the air.  They will freeze for a couple of seconds, then Rolo will walk away like he's lost interest, and Peppermint will stay frozen and start pooping all of those really icky fear-poops that are too gooey to pick up easily.... and they smell really bad, but whatever.  And he'll stay frozen until Rolo starts the entire thing over again.  Peppermint seems terrified, and Rolo seems really anxious.  I don't knwo what to do- their little tussles can get pretty intense, too.  When I picked up Peppermint today, I saw a little cut on his back- it didn't look too bad, and it was really tiny, but still...
This is only my third time putting them together, but it just doesn't seem normal.  Is this what rats always do when they are new to one another?

[JR1030]

It is pretty common for tussles to ensue to establish the pecking order, so to speak.  How old are your boys?  And do you have water in the tub when you do that?

[Kendra]

You might consider putting a little vanilla on each rat to mask their scent.  Have you been putting cloth from each cage in with the other rat?

[Ratskateer]

no, there was no water, and I've been doing the vanilla; I'll put some cloth in, though.
My boys are 15 months and 5 months.

[JR1030]

I actually do intros in the tub with water in it, and a little "island" in the middle with some yummy food.  It seems like trying to get away from the yucky water, and eating the yummy food can be a bonding experience for them.