AE
Are you SURE you have an M-25? And not an M-25XP? The M-25 didn't come with a hose.
Do you have the manuals? Boat owners, engine ops, engine parts, engine technical?
The hose fitting on the M-25XPA is 1/4" NPT, but that engine was by Westerbke (after it bought Univeral Medalist.) So I can't verify the size used on the earlier engine. It MAY be 1/4" but the XPA hose is a different part # so who knows.
For my money, if I had the drain hose I would put a female quick-connect on the end and a male end on my pump hose (or on a barbed fitting so I could use a throw-away hose) so I didn't need to mess with the fitting anymore. I use a 12/ impeller pump that I suck thru the dipstick tube (or "guide, oil" as Kubota calls it.) It is a multi=purpose pump I have set up for many uses on the boat. I bought a Worst Marine 12v pump and it lasted 2 seasons. I have used this one for 25 years.
It really helps if you put your boat, hull, keel, engine info ( mk-?, yr? tr/sr? bs? fk/sk/wk? hull #? etc.) in your profile or signature to help us help you.
Cheers, Ken