The medium is prepared differently for slants than Petri dishes. Sterilization is done with the agar in the tubes; Petri dishes are pre-sterilized before sterilized agar is poured into them. Measure the amount of water needed and put it in a pot. Heat it on a stove until it is almost boiling. Add dry ingredients and stir the mixture slowly until they dissolve. Before adding agar, mix it with a small amount of cold water to prevent lumping. Use caution when adding agar to the hot liquid since it can foam and overflow the pot. Add small amounts of agar at a time and stir to evenly distribute the agar. Turn off the heat after bringing the agar to boil.
Place test tubes without the caps on a test tube rack. Fill the test tubes by transferring about 5 milliliters -- about .17 ounce or 1 teaspoon -- of the molten agar from the pot using a pipette, a small funnel or a syringe. Place all the caps loosely on the test tubes -- the agar won't be sterilized if they are sealed tight -- and sterilize all the tubes for about 25 minutes at 250 degrees Fahrenheit.
When the agar is still hot, tilt the rack holding the test tubes on a solid surface or a thick book, making sure the medium inside the tubes is at a slanted position. Allow the medium to cool and solidify at this angle, which increases the surface area of the agar.
Tighten the caps of the test tubes after the agar has cooled. The slants are ready for use once the agar has solidified. They can be stored at room temperature or in the refrigerator for future use.
Inoculate the slant by transferring cells with an inoculating loop from a single-colony microorganism on a plate to the slant's surface. Move the loop across the surface of the slant and cap the tubes. Incubate the slant until there is evidence of growth, then put the tube in a refrigerator.