Assuming your drain is throttled or runs partial siphon (sucks air), put it on the drain, not the return pump. Adding it to the return pump decreases the flow through the sump as the return pump now has to push against extra resistance. Putting it on the drain side gravity is doing the work for you.
Downsides to this:
1) Obviously that doesn't apply if you are near capacity on your drain, but if that's the case you have a ticking time bomb anyways.
2) Doesn't get everything if you have more than one drain, although that does make it easier to tune flow rate.
3) Consider plumbing in a way that is both easy to drain when you need to open it and change the bulb as well as a way where it stays full if the return pump dies. There was a recent thread about this.