Bingo, with another brand, I shared a cubical with the Senior Removable Body Parts Engineer about a decade ago so I know the drill. Also don't hit deep water at speed now with the x flaps removed unless you are in need of a shower!

 

I worked on clearing the lines 2.5 hours today, no luck locating the line at the firewall. I worked on the passenger side and could see a part of the line only.
I decided that I would try and work backwards. So I removed the tire and tire liner, but could not still not see where it drained out.
Next option was to try and flush from the sunroof with a water squeeze bottle. I connected a plastic tube to the bottle and pushed the plastic tube into drain hole at the sunroof and squeezed. I did hear a sound like it cleared and did notice water on the ground. I did the same on the drivers side and also heard noise and saw water on the ground.
Only a temporary fix and plan to try again soon.
Any tips on following the tube on the passenger side, it seems to be the worst.

 

I went at it this morning following your guidance to stop the leak. What I found surprised me. The tube on the drivers side was not connected. Once I reconnected it drained fine. Have you ever read of a tube dislodging all by its lonesome.
Puzzled!

 

That's really odd because it is a tube and if it was not clogged and not connected it would have been draining in your car under your dash. If it was and reconnecting it fixed it yen great. If someone worked on your car they could have pulled it off? Who know but hopefully it's not draining into your car anymore.

 

I just did my wife's H3 front and rear sunroof drains. I ran 5/16 hose straight down and out through the floor on the front drains. The reason I did that is once I saw all the lines I found out mine also clogging up in the blends on the hard lines (not just the grommets) They were packed full. You also cant get anything through it to un-clog them later. Once I clipped the bends out (right at the dash), slid a piece of new flexible clear 5/16 hose on, drilled a hole in the floor behind the kick panels, added a little silicon, and DONE. You can put the old grommet back in the hole if you like. I can hold a water hose up on roof and watch it run out the tube.
I did the rear drains without removing the fender flares/Fenders. Just remove the bolts from the inner fender well, drop it down, reach up into the little grommet with an exacto knife and slice the end off of it. Then I took a piece of regular stranded wire and just pushed up through the hole to unclog the line. (it will come out up in the head linner area) Then I blew it out with the air hose. Remember the back ones will not drain sitting on flat ground (unless you have the front level kit) Jack up the front end or pull it up on a little slope and put a hose up there and let it run. You have to slice off the end of that grommet to let it flow out easily without getting stopped up.
That is my fix!

 

15 MINUTE FIX PLUGGED DRAINANGE HOLES
I had the same problem with my 2007 H3 with the Sunroof leak! The draining holes on both side of the front sunroof were plugged and no water was draining to the bottom of the truck.
I didn't want to take the whole truck apart so I tried a different approach and it seemed to work.
I thought maybe I could take a small flexible tube and vacuum the grime and dried dirt away that was plugging up at the grommets.
I went to the hardware store and bought 5 feet of flexible clear rubber tubing 3/8" diameter (the 1/2" was too big to fit through the drainage hole) cost was $1.50. I then got my wet/vac and attached the tiny tube to the big vacuum hose. To attach the tiny tube to the vacuum cleaner I cut out a round piece of pink Styrofoam and stuck it to the vacuum opening and then drilled a 3/8" hole in to the Styrofoam and slid the tube through the Styrofoam so there was no air escaping so that it would have stronger suction power. I duct taped everything together so there was little suction lost.
I then filled the sunroof drainage area with water and wormed the flexible tube a good 4 ft into the drain hole. I agitated the tube and then turned on the vacuum and vacuumed all the water out while the flexible tube was all the way in. I did this 2 times. On the third attempt when I poured the water through the drainage area the water started to come out of the bottom of the hummer on its own. The passage was getting clear.
With new found hope I did the whole process a few more times on the same opening until the water completely disappeared when I poured it in.
The opening seemed completely open because the water drained out immediately.
I then did the same process to the other side with the same results. Now both sides are freely opened and draining out water as before.
No more wet Interiors!
I think I will somehow try to put a small screen over the drain hole somehow to stop crap from going down it like they have in kitchen sinks.

 

I got soaked last night...again! Will do some drain cleaning if it ever stops raining.

 

New owner of a 2007 H3 Luxury, after reading the entire thread I performed the suggest surgery on both drain tubes yesterday afternoon, took all of about 30min. for both sides. I did add a little white lithium grease to the backend of the grommets and they popped right into the firewall with no problems. Ran a couple of gallons of water over the sunroof and everything drained out onto the drive. Glad I got this taken care of as we have rain forecast for every day this next week here in OKC.

 

Gonna do this fix tomorrow but I have a big question: if I have water on the floor AND dripping from the On-star mic, isn't the drain tube disconnected somewhere in the roof?

 

Nope. The tube is clogged at the bottom where the 'X' is and the water is backing up the tube and overflowing into the sunroof trough and overflowing into the headliner.