Oil for handpump

Hello,

So I use a Chinese Bull pump to charge my PCPs. I regard the Bull pump vastly superior to my Hill MK3 pump.

However, the Bull pump needs to be liberally lubricated with silicone oil ( the manual sates this). I actually tried grease: the pump stops working.

But when I bleed off the air, some of the blackened oil comes out (it clearly contains carbon deposits). I also noticed that my Theoben Rapid had black crud on the inside.

Am I using the wrong oil? Should I use an oil separator?

PS: I am using a generic silicone oil.