Repurposing the high pressure oil pump on the burner
Normally the oil pump is used to create a high pressure oil feed to the nozzle causing the nozzle to atomize and spray the fuel out as a very fine mist.
However, in the modification of the burner, this pump is no longer used with the nozzle and the line to the nozzle gets removed and the oil pump hole is then plugged. The pump will now be used to help filter the dirty waste oil. Since the new siphon feed nozzle has a much larger nozzle oriface, the oil does not have to be filtered as fine as it does when using the regular nozzle. For the Delavan .5GPH nozzle I use a mesh #50 stainless steel cleanable filter. I'm using the Action AFI-1.0-50 1" 50-Mesh Irrigation Filter which is under $50. See http://www.homebuilderwholesale.com/ACTION-AFI-1.0-50.html. A slightly finer mesh filter may be needed for higher GPH siphon feed type nozzles.
Notice the white cap on the bottom. I unscrew & remove this cap and screw on a 1/4 turn brass ball valve. This allows easy draining of the clear bowl before removing it to clean the internal mesh 50 filter screen. The waste oil feed line from the main waste oil tank is now connected to the Input of the mesh filter. The Ouput side of the filter is then connected to the oil pump input. The ouput of the oil pump is now sent back to the main waste oil tank. However, there is a "T" in the line to also feed the preheat/constant level tank. Thus the pump is now only used to help filter the oil and to supply oil to the preheat/constant level tank. The return line from the "T" back to the Tank must rise higher than the top of the Preheat/Constant Level Tank so that oil will be supplied to it's float.
Also notice that an oil "puckup" tube will need to be installed that reaches close to the bottom of the tank. You may want to stay about an inch above the bottom of the tank to allow room for any water to settle which can be pumped out every so often depending on how much water you have in the oil. The return line from the pump just dumps the oil back in the very top of the tank. I recommend a 3/8 OD copper pipe for the "pickup" tube. The "T" line connects to the float valve fitting of the Preheat/Constant Level tank.
I like to the 275 gallon Poly tote type tank for a main tank. These can easily be found used in my area for about $40 - $80. Notice the red screw on/off lid and the nice galvanized metal cage. I like these because when they're empty, they're under 120lbs which allows me to load/unload them from my truck by myself. Remember that if you fill one of these full with waste motor oil, at 7.35 lbs/ga, that it will weigh over 2000 lbs = 1 TON so be sure to have the appropriate truck if transporting the oil!