I used to do partial mashes in a 3 gallon cooler that I got for cheap and lined with a 5 gallon paint strainer bag. Since this was usually 7lb of grain max I would just lift the bag a little and collect runnings from the unmodified spout (then batch sparge and repeat). Consistently got 75-80% efficiency this way. I have used the oven technique too, though, with good success. I would recommend one of these ways rather than trying to direct fire a small pot.