No-pump hand wash system
Here is a picture of my gravity-powered hand wash system. It consists of 2 buckets and a feed scoop with a few holes drilled in it. I cut off the lip of the feed scoop to fit better into the upper tank bucket. Just dip the scoop into the upper tank bucket and hang using the handle.
It is inexpensive ($6 scoop at your local ranch store), light, works with any style of bucket and does not have parts to break, freeze or get mucked up with sand. Stack the buckets, drop the scoop and soap into the buckets and place in a medium-sized roll-top dry bag for a contained unit and last-minute loading on the boat.
It is old school for sure but it works great.