CREATE TABLE table_6494 ("Tie no" TEXT, "Home team" TEXT, "Score" TEXT, "Away team" TEXT, "Attendance" TEXT)

Which Tie # has an Away team of slough town?
SELECT "Tie no" FROM table_6494 WHERE "Away team" = 'slough town'
SELECT "Tie no" FROM "table_6494" WHERE "Away team" = 'slough town'