I find it imperative to have sap trickle into the pump during slow periods, slow meaning when sap will sit around on gravity or not even flow.
Slow periods is when the pump is really important. I suck sap from my collection tank (just a bit) and just return it to the collection tank(full cycle). Doing this gives more vacuum to the lines in the bush. Also keeps the pump drinking fluid/air at all times. Again, only when sap is not flowing good on its own. A good flow day I do not suck from my collection barrel.

I use a manifold on my pump and it works great, you do need to babysit it though during slow times to fine tune it. If sap is running good, just plug and play.

Hope that makes sense.