TH scuppers

[tagalong]

Couldnt find much in search mode,so has anyone tried the TH thru hulls for below waterline applications. As I said, its a 74 23 center console. the vertical scupper drains don't drain worth a crap. One bubbles up 2-3" od water at cruising speed and the other doesn't drain. The non draining one has what looks like some kind of white plactic backflow preventer in it. Is this some type of ball valve, or is it a bottle cap? I have been lookin at the TH underwater thru hulls(out the transom) and wondered if anyone had any dealings with these.

One last question, This boat is a '74. Factory floor has that striped non skid pattern, right. This one has smooth floors with painted nonskid. Is this a replacement.
Any help would be appreciated. Possibly buying this boat in the next few days, but really dont want another boat with floor draining issues.

Thanks in advance!