What were they thinking when they designed the Catalina 22 galley without a drain for the water tank? All RVs have them. They’re essential to keeping the water fresh, make sterilizing and flushing the tank easy enough to actually do from time to time, and prevent biohazard from growing in the tank, supply tubing, and pump like this:
Go to the RV parts store first, not last
So when I set out to replace the bacteria supply tubing, I decided to solve the drain problem at the same time. I couldn’t find anything that would work at West Marine, so I paid a visit to my local RV parts store and picked up a small plastic drain valve and matching nut. The valve has a 3/8″ barb on one side and a 3/4″ threaded nipple on the other. I drilled a 7/8″ hole in the fiberglass sink cutout that’s glued to the bottom of the galley. Not sure what that’s for. The hole needs to be as close to the sink drain tub as possible so that it will also drain into the funnel below. I mounted the valve in the hole and connected the valve to the new fresh water supply tubing with a 3/8″ nylon T.
To open the valve and drain the tank, I simply pull the drawer completely out of the galley, reach into the right side of the galley with my left arm, and feel around to find and open the valve.
Now the water we’re drinking should be a bit more healthy than the water we’re sailing in. For more galley mods, see Make Your Galley Easier To Slide & How To Replace Old Drain Tubing.
The $tingy Sailor 
My sink drain hose also needs to be replaced. What is the measurement for the amount hanging into the funnel under the galley or is it non critical? I will have to find an online order source for this drain valve because of my location. Do you have a source suggestion? Thanks James
The length isn’t critical, just enough to reach from the sink drain nipple through the bottom of the galley. I’d guess it’s less than 18″ and depending on where you buy the tubing, they might only cut to 1′ increments so 2′ would more than enough. I bought enough to replace the scupper drain tubes at the same time and probably bought 4′.
I found that valve sold online as part 25748 here: https://www.rvadenver.com/new_page_30.htm.