public List<T> GetAllItemsFromBucket(string bucketPath)
{
    var index = ContentSearchManager.GetIndex("{index name}");
    using (var context = index.CreateSearchContext())
    {
        var results = context.GetQueryable<T>().Where(x => x.Path.StartsWith(bucketPath)).ToList();
        foreach (var result in results) _service.Map(result);
        return results;
    }
}

IIndexable index = new SitecoreIndexableItem(bucketItem);
using (var context = ContentSearchManager.GetIndex(index).CreateSearchContext())
{
    ...
}

string query = string.Format("fast:{0}//*", bucketPath);
var items = SiteContext.Current.MasterDatabase.SelectItems(query);