Hey There!! :welcome:
Many Pro's here to help you out!
I'm not a pro, but I think I can help with this one anyway..
I suppose you could without the tools, but it'd be waiting for air to escape, wondering if it's really full etc..Then when you think it's full, you run it, gears move, air goes to top and now it's not full anymore, and toasted lower unit......
Why do that?
Most lower units have 2 screws.. A vent (top) and a fill/drain (bottom)..
With both out, plug one of these:
https://www.iboats.com/shop/seachoic...3-1-2-gpm.html
into the lower (drain/fill) hole. Pump till it comes out the top..
Then put plug in the top, remove pump fitting and install drain/fill plug..
Making sure you have fresh washers/gaskets on both the vent and fill/drain screws..
These hand pump things are only about $6-$10US depending on where you get one..
(May even find them at local box stores too.. Can't say for sure.. )
In short, yeah.. you need the adapter of sorts, and for the money, it's really a VERY small investment to get it filled properly each time and not have to worry about it. IMO..
Hope it helps!