Your hospital should have a written policy regarding flushing NG tubes.. That being said, if the obstruction is lessening there may not be any drainage. The NG may be blocked, if it's on continuous suction (that's how our physicians order it) it may be against the wall and the patient may need to change positions, or flushing may change the position (some will order intermittant suctioning just because of this). If it is a small-bore NG tube there may be particles too large for the tube that are blocking the tube; flushing will also help there, although changing to a larger size NG will help more-I let the physician decide. If the obstruction is resolving, there will be little or no drainage. Is the patient uncomfortable? Nauseated? Then check placement and flush. If the patient is not uncomfortable, you can still flush, but the amount of drainage may not increase.
I find it can also help if the canister is placed on the bedside table vs the wall.... sometimes with low suction it doesn't have enough oomf to pull it up to the wall. You can also try switching it to Low Intermit Suction for a time and see if that helps.
If you have a Salem sump you should have it on low continuous. The reasoning is that salems have two lumens, the blue one is for venting the tube. The venting action keeps the tube from suctioning against the stomach wall and negates the need for intermittent suction. Also, with a salmen if the tube is not clogged and is positioning properly in the stomach you have no need for an anti-reflux valve as well.
if you find no drainage from a salem, simply use the blue port and instill 30 mls of air into it. If this increases your drainage you had one of the few times a salem sucked up against the wall. If that doesn't work then instill 30 mls of sterile water into the main lumen and watch for return.