I was thinking about connecting my drain line straight to a Octopus 150 recir skimmer then have it dump into my sump with fuge. Plan on having ball valve on drain to control water flow. Is it possible without have major issues?
Many people do this the only thing is to make sure that your drain won't overflow the skimmer. The ball valve will help however it may be necessary to split the drain so that part goes into the skimmer and the rest drains into the sump.
The key is to have a T off the main line with a ball valve before the skimmer. The skimmer should be fed off the vertical T-junction, with the horizontal T-junction going straight into the sump. The idea is to maximise the distance between the T and the ball valve in order to minimise surging in the skimmer (which would create turbulence, adversely affecting skimming). You use the ball valve to control the water level/flow in the skimmer to the desired level.
Maybe you can put that "T" in the vertical position, but have the horizontal go to the skimmer and the vertical outlet of the "T" would be at the desired height of water in the skimmer. IOW, any extra water (more than we want in the skimmer) will go to somewhere else (in the sump).
If the "T" is down near the inlet of the pump to the skimmer that "T" could be made say, 10+" tall with some pipe so any little surges in flow to that "T" would be balanced within the vertical pipe of the "T".
If you make the skimmer feed the horizontal junction then the skimmer does not get priority flow and the water may simply bypass the skimmer and go straight down into the sump - you should make sure the restricted line (i.e. the skimmer feed line) is the vertical junction. The idea is to constantly have water in the pipe above the skimmer so that there is a smooth, steady flow. If the pipe overfills then the water simply goes via the other junction of the T right into the sump.
I have my overflows plumbed directly into the skimmer and flowing into the sump with no issues.
I'm using a Mag 9.5 as the return pump and controlling the flow with a valve on the return to the tank. I had to reduce the flow slightly on the return in order to prevent the skimmer from overflowing.