special sandbags for weighing down a tripod

I'm not sure why you would need one for each leg? When I need the extra stabilization, I hang a full, one-gallon water jug from the center column by a bungee cord, and that works very well. Besides, both the water and the bungee cord can be useful for other things when on the road...

There are several brands of sandbag for the center hook, I think at least Manfrotto made one type.

Good pt on the water, I didn't realize companies actually made special bags, lol. I searched adorama and found plenty of results.

I made my own out of PVC Pipe. The first one that made was 1.5 inch PVC, then I made one later with 3". Put a cap on the bottom, Fill with something heavy (I used lead shot), in the top, screw a eye bolt, (put on locktite on the bolt on the inside to make sure that it does not come loose), and then you can thread some webbing with a quick release, to hang from a leg, or just use the eyelet on the hook of the center Column. I have been meaning to make another one with a screw connection so I could fill it up with water, sand, or rocks when traveling and not carry that weight around.

The water is a good idea, but if you want sandbags, check a film/theater lighting and grip company. I got several sand bags from one a long time ago. They have a velcro closing strip and I can empty and film them in the field if needed. These work great for when I have to fly somewhere on assignment, I can find any home improvement center and buy a bag of sand or just fill it on location if I need to hike in somewhere. On the other hand, I have never actually found it necessary to sandbag a tripod--light stands are another issue! --and yes, you need only weigh down the center column, doing the legs does nothing if you are looking for extra stability!

You might even just use a dumbbell of about five pounds with a tether wrapped around one of the ends. And if you buy two,ho ho, you get to practice bicep curls with them. Obviously not an air travel idea. I use two thre pounders covered in a neoprend foam and one in each side of a saddle bag affair to hang on things works not bad...who needs sand and mess I am thinking...I know it makes sense I guess on beach shoots...and always there is the hang your camera bag on the thing somehow. my old..manfrotto pod has a little hole on the platform right to tie a lanyard. no hook on it, but it works to steady up and stop the vibration quicker and is low enough as I choose to hang it to center of mass of the whole affair. See an idea tip a day on PN.. and all for free. and some might even work,...

Many, many years ago when I used a tripod with a geared column, I drove a tent stake with a nylon cord into the ground and attached it to the hook on the center column.

Raised the center column, just a bit and the whole affair was locked down tight, and quite solid.