Eric, The thru hull is quite small.
It is probably 3/8 to 1/2 inside diameter at the most.The clog is probably one of two things. A clog from something in the sink like grease or that run away pasta that has swelled or just gunk build up. The other possibility is the exit hole is growing closed with marine growth.I would take the hose off the sink. The end of the hose is still above water level. Take about a three or four foot length of 12gage insulated solid wire. Bend the end back on itself, crimp it so that has no loop. Tape the end with a few wraps of electrical tape so that it doesn't hang up during the following proceedure.Push the wire down the flexible hose and through the thru hull 4 or 5 times and then remove the wire. Hook the sink up and it should drain.If the hose isn't to nasty, you could even try blowing through it.r.w.landau