fresh water tank plumbing

[batt]

I am redoing a 74 trade wind land Yacht , the plumbing was changed. I have pulled the tank which looks good but I am not sure how to re plumb it. I am guessing the 1/2" outlet on the bottom is the supply which runs to a filter and to the pump. The other two fittings are 3/8 " nipples on the top either side of the center of the tank. I read that these were vents which are meant to T and run somewhere to the underside of the sink. could someone elaborate on this? AS I say I have nothing to go on. I have the old pump sitting there which I plan on replacing with a new quiet one.

Is 1/2 pex adequate, I am guessing it would be, since none of these fixtures draw much.

[DanielB]

Here is the fresh water page from the service manual for a 25'.
It doesn't show the two relief hose things. they come up from the tank and come together with a T then the one line goes on the nipple thing directly underneath the input hose where the water comes in.