Prime the Nozzles?

EGropp

I have a 3 extruder setup and wondering how i prime all 3 nozzles at the beginning of a print.
I have it setup now to heat the bed, then heat the extruders and when everything is up to temp, it homes the axis. If i dont heat the extruders and there are remnants of the previous print, homing the z axis causes the head to push the bed down and the z-home sensor never activates.

Now that this has been corrected, what would be the best process to prime the extruders before a multi material print? There seems to be maybe a bit too much retraction at the end of a print as a new print does not seem to start nozzle 2 and 3 with the filament in place. The skirt actually primes nozzle 1, there are 2 loops for the skirt and the material actually started to come out just past midway on the first loop. 
when the second and third nozzles start to print, there is nothing coming out for a short time.

What is the best (most efficient) way to prime the nozzles pre-print?

Repetier

Normally you have a prime/wipe tower for this where it prints until filament is coming as supposed, then go to real object for clean print. You need to use slic3r prusa edition added in 2.0 host versions to get it. Make sure nozzle size is 0.4mm. Works only with some conditions but you can google that.

EGropp

I have been looking through the different slicers to see what i can make happen for a prime/wipe tower. 
I can only get it to actually show up in the interface if i use the Slic3r prusa edition, but it shows only 1 tower. I have 3 extruders on this machine.
Have i missed a setting somewhere?

Repetier

Have you checked if they share the prime tower? For 2 color prints you need only one and for 3 you might share areas, but not sure that prusa does here.