Can sterile normal saline be used for IM injections into human buttocks just to practice injection technique? person is very healthy how much...

It is safe to inject small quantities of sterile normal
saline into the buttocks using new disposable needles and syringes, and doing so under
supervision of a nurse or physician instructor.  I would recommend using about 0.5 cc
for each injection.  You can practice either subcutaneous injection into fat, or deeper
intramuscular injection.  Both techniques are used medically depending on medication and
circumstances.

Do NOT use sterile water for injection
practice.  Water injections are painful!  And because water is hypotonic compared to the
blood and tissues, the water will cause hemolysis (rupture) of blood cells and lysis
(disintegration) of tissue cells.

Using 0.5 cc sterile
normal saline, you can very safely inject several times with no adverse outcome other
than the minor “prick” from the needle.