[RayChez1]

The little water drains in the manifold area are for the water in the water lines, not the tank. The white plastic cap is when you remove the filter, you replace the cap where the filter screwed on to.
Not sure where the water drain is for the big tank, but if I wanted to get rid of the water in the tank just pump it out. There is a faucet on the outside where you can just pump it into your grass or down the sewer drain. I never have looked for a drain on mine because we use the coach all the time. We live in California so we have good weather all the time and many places to go to. But I am sure there has to be a big drain valve somewhere. Check your manual or call Gulf Stream they will usually give you the info you need.