[deepsushi]

I have both the thru hull drains as well as scuppers out the back on my inboard. The thru hull ones work well to drain when at the mooring but need to be plugged when running.

My scuppers that run out the stern sit right at the waterline. When the boat has full fuel tanks I can get some slight water come back through the scuppers.

I think changing it out to the "regulator style" (google it) thru hulls and some fiberglass oval tubes might be the way to go.