I'm trying to rotate the water pipes (like you see in 2fort) at a 5 degree angle,but the problem is no matter what I do I just can't get it to line up with the grid in hammer. Any ideas?
What pipes are you talking about exactly? Screenshot, or model name please. Or are you talking about sewer pipes?
You can hold ALT when moving or rotating objects - this allows you to move things off grid. While this is ill-advised for brushwork theres no problem with props (and any other point entity for that matter) being off-grid.