I've stolen this from Erowid. I've used this method before and it works the trick is to grind the pot properly;

To make a basic solvent-extracted 'hash' from dried leaves or dried buds:

Take dried marijauna and crush it up into a fine powder.

Put the powder in a jar with 100% pure Isopropyl alcohol, so the alcohol covers the powder.

Soak in a dark place for anywhere from a couple of hours to a few days.

Pour the mixture through a screen onto a glass plate. A fine kitchen strainer or gold coffee filter work well.

Evaporate the liquid carefully. This can be done either by letting it sit out in a warm place or by heating it up. If you're going to heat it, be careful: it's flammable. Do it someplace with good ventalation, preferably near a kitchen exhaust fan that blows outside. A fan blowing over the top of a pan will speed evaporation, but can increase risk of fire.

Please Note: If alcohol or any flammable solvent is used, a fire extinguisher should be on hand, there should be consistent ventilation to keep fumes from building up, and open flames should be avoided. If heat is to be used, electric burners are far preferred. In a pinch, damp towels can be used to suppress flames on a pan, a metal pan lid to fit tightly over the pan being used, or a bucket of water. Even a spark from an electric fan can cause a fire and could result in a primitive flame jet.

Scrape up the tar with a razor blade or spatula. Try to choose a pan or bowl that won't be harmed by a razor (glass?).

If it is too sticky, add a little dry powder till it attains the consistancy of silly putty. Work it over and over. This seems to make it bind together. Practice makes perfect.