How do I bid using "weak Stayman" (or garbage stayman)
One you have decided to bid a weak Stayman, it is imperative that you pass opener's rebid. 

Any subsequent action of any sort by your hand categorically promises 8+ points.

Consequently, you must have a hand that can tolerate any of the three acceptable responses to Stayman. It is unwise to make this bid with club tolerance for two reasons:


Partner responds 2D too often, and you have jumped into an inferior contract that is easier for the opponents to double than was 1NT.
You lose the valuable inference from the auction following that you have either a few points or club tolerance or both:


  1NT    P     P    Dbl
    ?
  
  It is possible to play more complicated sequences in these situations, but they must be very well discussed with partner. It is extremely demoralizing for a partnership to be at risk of 500 or 800 point sets on every 1NT opening, due to bad experience with toys like poorly agreed weak Stayman.