Suction
Suction is a (restricted) defense against 1NT that does not promise an anchor suit. Each suited overcall shows the next-higher suit OR the other two suits. The suits "wrap" so that

| Dbl | Clubs + hearts |
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Diamonds OR hearts + spades |
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Hearts OR spades + clubs |
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Spades OR clubs + diamonds |
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Clubs OR diamonds + hearts | 2NT | Diamonds + spades |
Responses
In response to Suction, advancer usually assumes a one-suited hand, and bids that suit. If overcaller has only shown a two-suiter (i.e. Double or 2NT), then advancer usually takes a preference in either suit. Any other bid by advancer is natural.Other Considerations
The benefits of Suction:- Suction provides a way for all one-suiters and two-suiters to be shown.
- Suction can cause headaches for the opponents. What does a double mean? A cue-bid?
- Unlike other defenses to 1NT, certain hands can't be shown at the 2-level, e.g. a club one-suiter or a minor two-suiter
- Suction is not permitted under the ACBL General Convention Chart (GCC), which says that two-suited overcalls must show "at least 5-4 distribution in two known suits."




