The vacuum is needed at the tap hole, that increases 5-7% more sap on average for each inch of vacuum on the tap hole. When you get to the mainline, which must be sloped downhill as Thompson said, you then drain the lateral into the mainline. For that you want a saddle and a connector. If you run the mainline tied to a tight support wire, you hook the connector to the wire, then a loop of tubing with no tension on it, curves around and connects to the saddle. If you are using the Rapid Tube method, with no support wire, use a length of the flat chain type strap used with RapidTube, hook it around the mainline with a tail facing the uphill incoming lateral. Attach the hook connector into an open space in the strap, then have a loop of tubing from the connector to the saddle. You need to understand that 3/16 requires cleaning. Clean it shortly after the season and again in mid to late fall, when temps are above freezing. I use calcium chloride, you can use sodium chloride but it can often attract squirrels looking for the residue salt.
I use 5/16 drops and 5/16 loops and saddles on my 3/16 laterals.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.