Before you use a solvent, make sure it's safe for the purpose and isn't going to damage your gun. These substances are typically flammable. If used for the wrong purpose they can combust or cause an explosion. Common uses and potential issues are described below.
GUN BORE CLEANER : Standard bore cleaners are used for steel barrels. A bore brush can be dampened to help remove rust and heavy residue. Patches or cleaning pellets lightly dampened should be pushed or pulled through in the direction ammo travels. Dry ones should be used to remove remaining solvent. A light coat of oil should be applied after cleaning to inhibit corrosion and residue. Some should be left dry after cleaning, this generally pertains to high-precision firearm barrels. In those cases no oil should be used after cleaning until the barrel is thoroughly broken-in, then dry patches should be used after oiling so only residual oil is left. These cleaners are corrosive to brass barrels and other parts made from or plated with soft metals. Brass barrels should be cleaned with oil only and metal brushes should never be used. Bore cleaners are generally flammable, make sure they don't get into parts that will be exposed to high pressure other than the barrel.
PENETRATING OILS : WD-40, Liquid Wrench and similar petroleum solvents are highly flammable. These should not be used to lubricate any part of an airgun, tank, pump or introduced into any pressurized component. If used as a cleaner they should be thoroughly removed from all pressurized parts or an explosion could occur.
ACETONE : Commonly used to clean metal parts for touch-ups and refinishing. Many plastic parts, paints and coatings are easily dissolved. This includes grips, forearms and some of the markings on sights. Acetone is flammable and the fumes are explosive.
ISOPROPYL ALCOHOL : Commonly used to clean parts, removes oil and grease. It won't dissolve plastic or paint. It's flammable and can produce explosive vapors.
DISH SOAP : This is an excellent parts cleaner that dissolves oil and grease. It can be used undiluted or mixed with varying amounts of water and easily rinses clean. Steel parts should be dried immediately and oiled to prevent corrosion.