In a large colander toss the cucumber and onion with two tablespoons of salt and let stand 10 minutes.
Rinse the cucumber and onion and drain well.
Meanwhile, in a medium saucepan, combine the remaining ingredients and bring to a boil, stirring to dissolve the salt and sugar, remove from heat when dissolved. Add the cucumber and onion and let cool completely.
Pour liquid over sliced cucumber, stir and store under refrigeration until needed.
Transfer the pickles to a siphon and charge with two charges. Shake well and refrigerate for 20 minutes.