So I need to run my 7.4L on trailer and at least adjust timing and a beginning of carb tuning. I'm not to sure if running on muffler will provide sufficient lube for the sea water pump tho. I just changed it and don't want to burn it out ....so muffler or tub of water with the outdrive submerged in that? Thanks

If normal water pick ups on the outdrive, muffs on the hose should be fine.
Hopefully you did something to lube the impeller for start up...?
I usually add some grease or have even filled housing with dish soap after installing new.
(Nice bubbles at start up )

Muffs are fine long as you stay at idle

The pump is new as of last fall , so a few runs on it. And I might need to rev a few times and pop it in gear to see what the engine does, since I changed everything on this boat except the main engine internals. So I need to get some base carb settings and timing done . Hence the concern muffs might not suffice ?

Reving up and back down won’t hurt it. Holding RPM very far off idle the pump will pull more water than the hose from your house can supply.

FWIW I've done both, the tub has been better for me.

I don't know what putting the drive in gear out of water will accomplish. There's no load. Better to fine tweak on the water? Let us know what happens

I did the 100 gal tub method once. That boat had factory thru the drive exh ( Alpha) so virtually all the water got recirculated. After abt 10 mins of idling, there was steam coming off the tub. Been using muffs ever since. If you put that thing in gear with drive in a tub, that full tub will be almost empty in abt 1 second. Guess you could remove the prop, but that's even more effort.

On the hose, Ive taken my engs to 3k rpm just long enough to verify timing adv, so maybe 1 or 2 seconds. I've heard the garden hose can collapse if rpms are too high for too long but never seen that in person. At below abt 900-1000 rpms, no issues idling for 10 mins or more.

I like the idea of muffs since they force water into the dry pump before eng starts. If you attach the muffs from the front of the drive and route hose away from the prop you should be able to shift in and out of gear all day long.

Ok 👍 thanks everyone for the useful feedback. I'll probably just go with muffs and keep it as brief as possible.