What is the best thing to use to get a pipe rusted in to the pump out?

A big pipe wrench and heat. Maybe penetrating oil but I don't have much faith in penetrating oil. I don't know that I've ever had it actually penetrate. But I'll use it if I'm desperate.

If that doesn't work, saw the pipe off with only 3/8" of the pipe sticking out of the end of the fitting on the pump. Saw a slot in the pipe from the inside of the pipe using a hacksaw blade. Once you're almost through the pipe and only have the threads left to saw, use a cold chisel and hammer to fold the cut in the pipe to the inside. Once you do this and effectively make the pipe diameter smaller, it can be turned out with any wrench.

Looks like I’m buying a front housing. lol

Get red hot, then pour cold water on the pipe and wait to cool then remove with pipe wrench

Oil will penetrate rusted threads, just like sweat soldering a pipe joint. Heat till the penetrant oil smokes but don't burn off dry. Spray till it stays wet. Then repeat. 50/50 ATF Acetone is the machinist chosen home brew.

Kroil? YouTube reviews say it isn't that great but my experiences show it to be pretty mean stuff.

2x kroil !! what metal is the pump?

PB Blaster spray keep touching it up a few times a day.

Red hot then tapp with hammer as your putting the torque to the pipe wrench.

I try not to heat castings to "red hot" but usually heat up and use penetrating oil to quench. then I stick a big pipe wrench on it and tap the casting (gently) while applying pressure. After that I am usually poed enough that I just cut the pipe off and use the sawzall as I would a broken nipple.

heat the pump casing not red hot , when hot touch it with a piece of wax , it will draw in the wax like solder, works every time

be careful the wax will burn !!!!

PB Blaster was the ticket.

Nipple extracting tool