My question is 2 fold, first I am wondering how sinks with foot pedals that turn on and off the water work, because they are below the faucet and I though water comes out from the faucet because of gravity. A example of what I am talking about is here: Hands Free, Foot Operated, Water Mixing, Single Pedal Control Valve Unimax Plumbing #PLMA-24 (http://unimaxsupply.com/equip/sinks/footvalve.htm) My second question is I am thinking about building a camping sink made from 5 gallon buckets, as seen here https://www.youtube.com/watch?v=embBA1LASpA but it works with a foot pump that you have to pump constantly for any water to come out and it looks like not much comes out and it is very sporadic. I like the idea of shutting the water on and off with your feet (but not having to constantly pump it) so I am wondering if I mount the freshwater bucket on a table or hang it from a tree if gravity will make it so I don't have to pump the foot pedal, but just step on it like the foot pedal in the first link I posted. If that will work do I use the same foot pump they used or some different kind of foot valve, and what kind?

Unless you pressurize the water holding tank, you will have to use a foot operated pump faucet. In campgrounds, water pressure comes from their system. Notice in your picture that the sink has house water supply lines behind the pedestal. You can gravity feed the sink with any sink faucet, they make very small ones for campers.

Gravity sink: Exactly as you said. Put one bucket higher, connect it to a dispenser (faucet) that sits lower than reservoir. Turn faucet ON and water flows like from regular faucet. The video clip is nice, but seems to me to be kind of complicated, especially when you have to haul it around. Your idea is what I would do.

Foot Activated faucet: Those we install in doctor's office a lot. Basically, the pedal is installed in combination with special angle stops. By stepping on the pedal, you open angle stop and water travels to the faucet.

Foot Activated mechanism, as shown in your link, cannot be used for the same application as shown in the YouTube clip as it works on completely different principle.

Let me know how you did

Milo

Milo with the foot pump in the video, if I put the fresh water bucket up high, would I just need to step on the pump and hold it down to make the water flow or would I still have to pump it?

Gravity brings the water down. You don't pump it.

Yes I know, so what kind of foot switch do I need to shut the water on and off, do they make some sort of foot activated ball valve?

I am not sure you can successfully achieve what you want under just gravity. The foot valve used in doctors offices, as shown in the picture, will work. However, the water pressure needs to be great enough to push the water through. By using a gravity system, you will not get enough head pressure to let it drop to the foot valve and then back up again unless you hang the bucket 10 ft. in the air! I just used an elevated bucket on a shelf and a 1/4 turn angle stop for a small faucet. Remember 5 gals. of water is 40# plus the bucket.

I did something like this to rig a shower while camping remotely! Wouldn't bother for washing up though.