shop-vac

A thing, situation, or person that both sucks and blows (i.e., REALLY sucks). Named after the shop-vac vacuum cleaner, which can be set to either draw air in or push it out.

When a dirty, talented tramp stuffs you're entire package (balls and all) into her mouth, and blows you with amazing suction power.

A powerful vacuum used to clean up large messes

When a girl is that big of a slut, shes sucking dick like a shop vac. Or when you suspect a guy using a shop vac in order to fulfill his needs

Sexual Act Only Capable of Being Preformed by the Talented:

A male or female human, and/or animal forms a tight seal over the anus of his or her sexual partner (usually with the lips of the mouth--though the differing biological attributes of species may change this slightly, e.g. elephants may use their trunks) and attempts to suck all accessible fecal matter from the consenting colon into the mouth.
Due to the high volume of pressure, any gaps in the seal tend to produce a sound which in addition to the act is similar to that of a ShopVac.
To aid in the facilitation of procuring large amounts of feces enemas may be preformed on the partner's anus prior to start.
Opinions differ on the proper disposal of said excrement after the process is complete. Some enthusiasts simply ingest though this is not encouraged due to increased health risks. Others attempt to force it back into their partner with mixed results depending on the consistency. Still others get more creative, painting their partners, putting it in or around their own anus, mixing it with various other substances. or vomiting uncontrollably.
Many of these fetishists are also very particular about what food they consume before the event. Very popular is performing this act while in the midst of a regimented colon cleanse.