What's with my grease gun?

Is lithium grease what I should be using, say for tie rod ends and
ball joints?

If there is leftover brown grease in the gun already, do I have to
clean every little bit out to use the lithium, or will it mix together
all right?

I cleaned it pretty well, put in a lithium tube, and after I released
it, somehow the plunger when almost all the way down. Is the new
grease too thin for the old tube, and now all the grease is behind the
plunger instead of being pushed by it? I pump the lever and get no
resistance and nothing comes out of the tube. I'm going to check
what's going on inside, but I want to do it outside and it's dark out
until morning.


Details if needed:
I got a grease gun at a yard sale, with a hose, and there seemed to be
no more grease in it, including when I opened it up.

So I got a tube of lithium grease. It wouldn't go in until I took the
plastic cover off of the one end, so the grease gun diameter isn't
very excessively big. I pulled out the plunger and latched it, put in
the tube, screwed on the head, released the plunger, and it went part
way down. I pumped the lever, and when nothing came out, I pushed on
the plunger a bit and with almost no effort on my part, it went half
way down. But still the lever worked just as badly. I pushed a bit
more and the plunger went all the way down. I pulled and it came all
the way back.

I don't want