I close all my thru hulls every time I leave the boat. So doing some work today, I opened the thru hull under the sink in the head and wondered why my hand was wet... Check out the OEM hose Hunter used for the drain:

No wonder I was seeing water stains next to the head. Anyway, all the advice I've read says you should only used heavy duty reinforced marine hose below the waterline, so I replaced this cr@#$p with the heavy black wire-reinforced hose you'd use for engine raw-water pickup, or other "serious" applications. Having just replaced 3 thru hulls this spring, I've already upgraded the raw-water pickup, macerator, and head pickup, but hadn't yet gotten to the galley and head sink drains.
It seems that those corrugated drain lines would be just as glad to sink the boat as any other below water line hose.

No wonder I was seeing water stains next to the head. Anyway, all the advice I've read says you should only used heavy duty reinforced marine hose below the waterline, so I replaced this cr@#$p with the heavy black wire-reinforced hose you'd use for engine raw-water pickup, or other "serious" applications. Having just replaced 3 thru hulls this spring, I've already upgraded the raw-water pickup, macerator, and head pickup, but hadn't yet gotten to the galley and head sink drains.
It seems that those corrugated drain lines would be just as glad to sink the boat as any other below water line hose.