first cut a rectangle twice the size of the wetbag you want to make plus seam allowances, mine is 12x6", it doesn't have to be exactly this size to be useful
here with the zipper that needs to be a bit longer then the short side of the fabric


pin the zipper to the end of the fabric, right sides together, the shiny side of the pul is the wrong side


sew it together and do the same with the other side
it should look like this


decide where you want the zipper, it can be anywhere along the bag, I like it just a bit off one end.
Pin it together,  make sure the zipper is open a bit so the pull is inside the bag and not in the seam, like this.


sew it together using a longer stitch then normal to make as few holes in the pul as possible, sew back and forth a bit over the zipper teeth to reinforce it,
like this


trim the zipper ends and zig-zag the seams


turn it right side out and you are done
run it through the drier to seal the holes from the needle,

it fits 2 pads nicely