db.js

'use strict';

var pg = require('pg')
  , bluebird = require('bluebird')
  , connString = require('./config').pg;

bluebird.promisifyAll(pg);
bluebird.promisifyAll(pg.Client.prototype);

module.exports = function() {
  return pg.connectAsync(connString).bind({}).spread(function(client, close) {
    this.close = close;
    this.client = client;
  }).finally(function() {
    this.close();
  });
};

other.js

var getDb = require('./db');

getDb().then(function() {
  return this.client.query('SELECT * FROM myTable WHERE pants = NULL');
}).get(rows).get(0).then(function(results) {
  // etc
});