I just tried this recirculating technique today (thanks Terry!). It works! Slow start and cloudy with 10", still some ice. After I let some sap into my mainline (just using a nearby saddle I added a 5/16 lateral with valve) it got the pump all serious and within 10 minutes of fiddling, I had 18". Things were still slow to start flowing, but with an extra 10", I'm sure it accelerated the process (and helped melt ice in the mainline near the pump). Pretty cool...

maplestudent, my pump is lower than the top of my tank and higher than the base. So I had to suck sap up, over the rim.