Sure you can make it work by running the hose through the hatch
It means having two people, one at pump
one at boat and a hose with shut off valves on each end.
Then connect boat hose to dock hose, open both valves on boat hose (and whatever valves are required dockside), pump
hazardous waste until tank empty. Shut off pump
, reverse pump to empty hoses as much as can be, close topside valve (boat hose) while pump in reverse, hold hose connection up so waste will not be at hose connection, close dockside hose valve, crack then disconnect fitting, continue holding both hoses up, shut off pump. Use pump person to cap dockside hose, wipe down the outside of hose as required, return to rack ready for next use.
While holding boat hose up, crack valve to empty remaining contents of hose into holding tank
, close and lock valve (you need a lock so valve cannot open when being moved around), wipe clean, install cap, secure hose end on deck so it does not fall down hatch
. Go to other end of hose while holding it so waste drains out of hose down to holding tank
and close hose valve at holding tank
and lock, with rag in hand disconnect hose, hold open end up, wipe clean, install cap.
Wipe down hose, place back in hose bag. Cap holding tank
fitting, wipe and clean top of tank, store hose bag on top of tank. Dispose of all rags, and if done properly there should be no need to wash hands...but do so anyway!
If you can develop and test such a procedure, and your other person is the type that can do such tasks, repeating back instructions, double checking each step, then it can be done and done right hundreds of times.
Of course miss one step, one time, and the expense of a proper install will seem insignificant, particularly after buying all the extra parts and hose needed.