Joe Manganiello Says He Had to Wear an Ostomy Bag During Batman Fitting

Joe Manganiello says he had an extra accessory when he was getting fitted for his Deathstroke costume ... the ostomy bag from his near-fatal health battle.

Joe mentioned the ostomy bag while recalling the stressful fitting for the since-shelved Batman movie Ben Affleck offered him a role in.

In an excerpt from his upcoming memoir, "Bloodlines," obtained by The Hollywood Reporter ... Joe says he stopped eating the afternoon before to make sure the bag was empty.

Joe wrote ... "I had to be absolutely sure nothing would come out in the bag while I wore the suit because under that degree of compression it would probably explode."

The actor said he was "appropriately empty" in time for the fitting, but had to act shy in the moment to clear everyone out of the room while he changed ... because he didn't want anyone seeing the bag or his surgery scars.

He continued ... "I confirmed that it was still empty—so far, so good—then I slipped into the bodysuit and called everyone back in."

Joe said the fitting went "as smoothly as could be" ... until they told them they wanted to do a 3D body scan and needed him to change from his black underwear to a pair of tiny blue briefs.

He said ... "I stared at them and began to panic. There was no way in hell that little thing would fit me, let alone hide the bag."