not mine...

Very cheap speedplay grease gun
https://www.youtube.com/watch?v=_x1hst38NpA

Low Cost Speedplay Grease Injection
https://www.youtube.com/watch?v=d2RWuzq-mFg

Speed Play Lube
https://www.youtube.com/watch?v=xa8Dv-V7a8Y

apparently it's best to rotate the pedals while putting in the new grease. i think i'm partial towards "marine grease", but i'm sure your favourite grease will work fine.

of course, DX has cheap syringes.