Get someone to help you so you can find the leak while another person
activates the tabs. If the tabs are not too far under and you can walk the
boat into some shallows so you can stand there is no reason you can't
replace the cylinder with the boat in the water. It will be easier is the
end of the cylinder is above the water line as you ought to put some bedding
compound where the screws go into the transom.

"Mike C" wrote in message
ps.com...
My trim tabs stopped working. I checked the fluid level, and it was
non-existent. I added ATF and switched on the tabs. The fluid all went
into the water. I believe only from the starboard hydraulic piston. I
have insta-trim tabs. I take it I have to replace the piston. How do
I do this? Does the boat need to be out of the water (problem!)? Is
there anything else I can check? There is no leaking inside the
engine compartment by the pump and I checked the hose connector to the
piston and it seems fine.