talked to frank the other day. saw it was pending sale a while ago so i asked if it was surveyed. he said the surveyor didn't know grady whites and said it had hull issues. definitely needs new transom, and stringers could be compromised with that much movement. boats only 20k, but...
There appears to be a sticker right before that "switch". which shows the direction for the valve to be in for pump out vs seacock. looks like lever may be thru the access pie plate on the wall under the sticker.
i just did mine on the starboard side so i didn't need the slider. But wife really likes it. mine is only supported on the top. The bottom doesn't quite reach the plywood base where the drawer was
put one on my 226 last year. seaspension seat pedestal. H can make it with the flat side like the original. wife says it take the edge off the slapping, which bothered her back. had to loose most of the space in the drawer underneath and with the swivel added about 1-2" in height.