I've been looking for some well drilling info for remote cabins. The link leads to a UNICEF document about some different primitive drilling techniques. If you are in a place where either 1)you can't mobilize a rig or 2) mobilizing a rig is more than you care to pay for a well, them maybe these will help.
THat is the link to the jetting document. If you have enough fluid velocity coming out of the end of pipe you can cut solid rock. I wrote an SPE paper about it. I think they were pumping on the order of 150 GPMs through a 1/2" orifice. Im not sure if a trash pump will provide the pressure, but you should be able to get that rate through a big hose. I was thinking a 2" jetting pipe that necks down to a 1/2" opening at 5,000 to 9,000 GPH inside a 4" well casing might work good. Some bentonite in your drilling fluid would really help wash the sand and pebbles out.
There are other techniques in that UNICEF series as well.