Sing does not drain with trap but does with straight pipe

How did you come to this conclusion ? Did you actually remove the trap ?

If it drains only w/o the trap than trap is probably full of food leftovers and grease. You can either clean it with garden hose and reinstall it - or buy new trap.

Curious, if you have a trap and then remove it the remaining two pipes will not line up straight down. Can you post a picture of what you are doing here?