I found it...
 

I was out last night and the drain plug and tether were
laying on top, now I know why it came back from 20hr
service with 1 plug missing, guess they didn't put it back.
seems like a good system to me. I'll let it drain while
I'm cleaning, I believe it is 9 quarts. I did the drill last time,
Thanks J.C.

I have NEVER been able to get out the last quart or quart & 1/2. The oil cooler, lines, etc. You'll be lucky to get 7 out of it. Careful not to overfill. I always go by dipstick (boat in water) anyway.

Interesting. I guess the positive slope on the racks at Marina Shores really helps. I just did my third oil change on these motors. 9 quarts every time. That puts the oil level just a bit above the full mark on the dip stick, but it came from the factory the same way.

not so quick oil update...
 

Seems like a great system, except fountain put the bilge
pump 1.5" from the drain hole. Took 30 mins just to get it
through the hole. By then it was dark so I let it drain all
night, At least I got it all out. Put 8.5 quarts in and still a
little low. I may not try this again.

If you let the motor warm up to operating temp on the garden hose prior to draining it, the oil drains out much faster.
I've changed mine twice in 50 hours. First cold and it took all night, second time I let it warm up and only had to drain for about an hour.
I believe Mercury recommends warming the motor first.

Careful on the hose. I found very poor water flow through my risers @ idle. You could have fried bacon after 5 minutes. Several folks report you need to run these up to 1500:eek: to get decent flow.

I've switched to draining @ the ramp after pulling out.

Wish I had a drain plug feature like that, would seem to have been the right way to go even 13 years ago when Merc made my motors (pair of 454 Magnums).

For 13 years I've been using the 5 gallon bucket and pump assembly and sucking it up through the dipstick after warming the motors up to normal temp. Gets just about 7 1/2 quarts out of the 8 quarts (including filter) in the 454 Mag. Changing every 30-50 hours max. 600+ hours, never a problem. The pump and bucket take about 3 minutes to 4 minutes to drain the pan, can change both motors and filters in less than 30 minutes when I'm in a hurry.

The bucket assembly is sold by people like BoatUS, but the one I have is homemade.