Technically you could get away with using 250mg every 7-10 days to preserve muscle. Most guys here use way more than that, even when cutting, but it's really unnecessary as Susta is more of a "mass" steroid. I think most here are going to tell you prop is the way to go, but if sust is what's available to you, then 1ml a week should be more than enough to retain muscle. Liquidex or Letro may be considered if you really want to keep the shredded appearance, although water retention should be minimal at that dose. Good luck