Yeah, I meant a 1/16" cable (sorry ...fat fingers!). I would get about 8' of cable. I think I paid 18 cent's/foot at a farm and barn store, it's not expensive. A person should get about 2' of 3/8 or 7/16" ID plastic hose to attach to the bottom of the drains while you clean them (or water will go on the floor).
Couple things I didn't mention about the cable worth knowing: 1) Get a rigid piece of straw (a straw from a can of Great Stuff work great) and put the tip of the straw partially into the drain hole, then thread the cable through the straw into the hole. It helps the cable keep shape and prevents a lot of monkeying around threading into the hole which is hard to reach. 2) When you buy the cable, you MUST tape the end yer cutting before you cut it (with a sharp cable-cutter). The end must be cut sharp and crisp, not frayed. Don't wrap tape too far (less than 1/2") up b/c the cable needs to remain flexible enough to bend around sharp radius'. 3) Wrap a piece of masking tape around the tip to make a 'rounded' tip so it doesn't catch and can slide around sharp corners as you push it down. I was going to braze some brass on the end of the cable and file it 'round' (like a B-B ) but I didn't need to. 4) I taped a small piece of plastic bag onto the cable and pulled it through while pouring warm soapy water on the hole. The plastic doesn't absorb water and expand like cloth does. But it does pull through fine and 'wipe' clean the inside of the tubes. After the first time I thoroughly cleaned the whole entire inner frame of the sunroof area b/c there was a lot of dirt in there. Then cleaned poured more warm soapy water and wiped the tubes again.
If you make a video, here are some things I would stress that I didn't see on most other videos:
1) The drains are a secondary water 'safety'. The sunroof itself shouldn't leak. If it' does, it's likely the gasket is ill-fitting or needs to be replaced.
2) Check the fit of the sunroof. Mine was very poorly fit ...angled down at the front where water would pool. Ideally it should fit flush with the roof or even a tad 'proud' to shed water off the roof.
3) Avoid parking your H3 on an incline with the front up, which would prevent proper water drainage, or you might get water on the floor anyway.
4) It's a good idea to keep the sunroof closed when not driving. Avoid parking under trees or any location where things (bugs/debris) might fall into it with it open.
5) It's not JUST the firewall grommets which plug up, the bottom of the tubes go horizontal before they go through the firewall. They should be sloped down a little more than they are. What happens is water is going to lose velocity in that region and allow sediment to drop and accumulate there. If ya park nose-up, then it's going to be like a sink trap and 'hold' water. Again, any sediment will accumulate there.
6) I'm not sure removing all the 'fingers' in the grommet is the best answer. If you cut them all out you can create a situation where insects can still get in. But it Will fix most of the drainage problems ...but bugs could come in. Will they? Depends, right? Another idea might be a hybrid idea -- to remove just ONE of the fingers with an exacto knife, and position the gromet with the open side down. That will allow water drainage and help prevent bugs from coming in. I've had in my Land Rover a similar situation where twice, bugs climbed up and built nests into the evaporator drain tube and caused water to back up and completely soak the carpet padding. So bugs CAN build clogging nests.
Anyway, those are just some thoughts I have you might consider incorporating into your video. There are a lot of ways to get to the finish line, I think most people cover them, but first and foremost is to fix the water intrusion issue through the sunroof with good gasketing.